For a dissapointing end boss fight I would have to say it was Dagon in the Elder Scrolls 4 Oblivion. You don't actually get to fight him, he's a giant 4 armed freky demon thing thats 10 stories tall. At first I was like ohh Sh*t this is going to be hard, but it will be interesting how I beat him. Then Martin turns into a dragon and POOF, Dagon is gone/dead. Seriously what the hell was the point of going on all those quests to stop this big evil thing and in the end not fight it (I will admit that most of the quests revolved aroung geting the amulet of king which Martin used to become the dragon so th the quests made sense in the end), but still could I have like fought Dagon while he is in a mortal form, then once I beat him he goes into an imortal form then Martin goes dragon and kills him, that would have not been so bad, at lest I would then get an end boss fight.

For a good end boss fight I would have to say Gongora in Lost Odyssey considering he was IMORTAL and had CRAPLOAD OF POWER and the ending was pretty good (kinda sad that Seth sacraficed heself to get rid of him though)

Good end boss: Ares- God of War 1. Epic in every sense of the word. Hard to kill, varied attacks, all of which devastating but none of them cheap. And...you're both about 100 feet tall...end of story. Oh, and he messes with Kratos's head, which is awesome.

Bad End Boss: The Controller- Armored Core 3: Err...hit the shiny things on the big pillar and....yeah thats it. >.<

Good end boss- the Boss from metal gear solid three (IMO)
Bad boss- Morrowinds Dagoth Ur who just needed a serious image revamp for him to pull of the whole evil villian thing, and Oblivion, who just didnt have one, cos Martin nicked all the credit! Also Tom Magruder at the end of Gun was a bit of a let down

EDIT: Aeviv beat me to it.

Good Boss - The Boss from MGS3: Snake Eater. There was a lot of emotion behind this fight given Naked Snake's reverence for his former mentor and the fact she'd kicked the sh1t out of him all the times before. The fight takes place with you being knee deep in a field of white flowers, with a few trees for cover. The whole thing is a game of cat and mouse as you try and draw a bead on The Boss before she finds you. Once she does, she rushes in for some CQC and it is very satisfing when you plant her on her ass using her own techniques.

Bad Boss - A second vote for Mehrunnes Dagon from Oblivion. He looks so intimidating, being 30ft tall and red, but it turned out to be not so much a fight as an "avoid and lead him over the the temple where Martin can turn into a dragon and kick his ass." Sure there are minions to slay but you can just easily run past them and continue on your merry way.

Good Boss: This one was tough but I have to say it has to be Sephiroth in KH 2 because he was enough of a challenge to actually be worth fighting to get one of the most powerful weapons in the game.

Bad Boss: I have to agree with the Mehrunes Dagon for bad boss freaking 30ft tall but you only get to fight his minions it disappointed me greatly.

I am a good End Boss.

Really, I enjoy pretty much most boss battles, except in most JRPGs. Or Judge Doom in Who Framed Roger Rabbit (NES).

GLaDOS was a cool boss battle, and I'm a huge fan of the giant ball of corpses from the Castlevania games.

Good end boss: Dragon Megumi, The World Ends With You.
You've got no partners, no fusion attacks, no light puck, no mercy. It's you VS a giant six-headed dragon. It's all-out through the whole fight. Unleash all your attacks at once then run around dodging like a manic while they recharge. Man, THAT was a final boss!

Bad end boss: Al'Mualim, Assassin's Creed.
Urgh. I beat the entire thing with the counter. The only challenging part is that he keeps teleporting all over the damn battlefield.

Good End Boss: If anyone has read any of my other posts this isn't really going to be a new thing I picked out of the air. The last boss of DrakenGard is still #1 for me.

Bad End Boss: hoo boy there certainly are no shortage of sad end bosses. Mostly from the FF series I feel. FF8's last boss was a joke. FF9's Last boss was so weak that the video on a monitor went out one time while fighting, and I kept fighting just using the sound, and still beat him, just to see if I could. However the cake has to go to FF7's boss Sephiroth. I was honestly expecting a LOT better from him. Threw out the game he was everywhere and always the best. But the last fight was just garbage. My first time playing threw I was pretty young, and didn't really understand the materia system, and only had level 2 or 3 limit breaks and I still beat him without any major problems.

Kikyoo:
Good End Boss: If anyone has read any of my other posts this isn't really going to be a new thing I picked out of the air. The last boss of DrakenGard is still #1 for me.

Bad End Boss: hoo boy there certainly are no shortage of sad end bosses. Mostly from the FF series I feel. FF8's last boss was a joke. FF9's Last boss was so weak that the video on a monitor went out one time while fighting, and I kept fighting just using the sound, and still beat him, just to see if I could. However the cake has to go to FF7's boss Sephiroth. I was honestly expecting a LOT better from him. Threw out the game he was everywhere and always the best. But the last fight was just garbage. My first time playing threw I was pretty young, and didn't really understand the materia system, and only had level 2 or 3 limit breaks and I still beat him without any major problems.

FF7 Really? I think it depends on level, I was probably the lowest possibly level to try and kill him, and he owned me time and time again. I never did get to a high level. Just got to a level high enough to kill him, barely.

Good End Boss: Ganondorf and Ganon from Ocarina of Time. He was challenging and fun, but still beatable with some effort on my very first try. I still say the attack where he charges up all those balls of negative light are the coolest things EVER.

Bad End Boss: That tick-looking thing from Final Fantasy X. You get infinite Reraise, so you can't die no matter what, and as long as you Zombie him, he'll just wind-up killing himself. Also, Vegnagun from X-2. "I will beat you buy attacking you with my keyboard-driven robot!" Needn't say more.

Good End Boss: Auuman Anubis (Zone of the Enders: The 2nd Runner). One of the most visually spectacular boss fights ever, he's also a tough nut to crack. This end fight was perfect to me, nothing in an action game can compare, in my opinion of course.

Bad End Boss: Yami Yugi (Yu-Gi-Oh! Dungeondice Monsters). This game really doesn't have a final boss since you run through different tournaments, but when you win enough games in a row, you play Yugi's alter ego. Man was this disapointing, I was hoping for the AI to be awesome and have some gnarly dice. But no, standard dice and the AI was no harder than the other lower tier characters.

Bad end boss: Sadler from RE4 all you had to do was throw a grenade at him to reveal his weakspot and then use your magnum to shoot it and then do the reaction command to climb on him and stab his weedspot again and if you run out of nades then u can use traps and if you run out of those shoot at his eyes on his legs (he just had too many ways to kill him).

Good end boss: The giant evil ball in Okami. It required u to use all of your abilities to defeat it and it was a pretty tough and long battle..

Good: GLaDOS, not to jump the bandwagon here but Valve basically owns my wallet.

Bad: Vamp from MGS4...

I played for 2 hours before looking up how to drop this sucker. I know he's not the end boos but this deserves mention, he's not even hard to kill repeatedly, but after so much of the shooty i had to do some weird crap with the syringe?

i knew i had to use the syringe but i had no idea how to do it, i had never done it or even bothered to grab someone until that point, great fight but poor design. i would not have minded if i had done it in the past or had been told about it in passing to preserve the feeling of 'Well what do i do!?' but to me it reeked of the developers having more fun than me.

Good end boss: Cubia Core (.Hack//GU Redemption) Challenging, but not "let me beat the damn game already!" challenging, and more importantly epic enough to be worthy of the last boss in a series of three games.

Runner up would be the final battle with Xemnas in KH2, sure he was a cakewalk but you have to admit some of the moves you pull off in that fight are sweet.

Bad end boss: Some Gnosis thing I don't even remember from Xenosaga Episode I... when you know a game is going to end awkwardly and you still think "...That's it!?" when you defeat the final boss and the ending starts, something went wrong.

Good: Dr. Nefarious b/w the Biobliterator from Ratchet & Clank 3
Bad: Dr. Breen; he just sits in some kind of time-space transcending bubble. But the play with the towers, energy balls and Overwatch Elite was excellent.
Ugly: Any Robber Baron in Sid Meier's Railroads on Mogul difficulty; not bad, but freaking hard.

Ultrajoe:

I played for 2 hours before looking up how to drop this sucker. I know he's not the end boos but this deserves mention, he's not even hard to kill repeatedly, but after so much of the shooty i had to do some weird crap with the syringe?

i knew i had to use the syringe but i had no idea how to do it, i had never done it or even bothered to grab someone until that point, great fight but poor design. i would not have minded if i had done it in the past or had been told about it in passing to preserve the feeling of 'Well what do i do!?' but to me it reeked of the developers having more fun than me.

Pfft, you must not remember people getting pissed off about Psycho Mantis, and then got even more pissed off when they realized that all they had to do was call the colonel to figure out what to do (and he simply tells you "Plug the controller into Port 2". I killed that bastard twice in MGS4 and then just spammed with Otacon calls until he figured it out. At least with vamp, chances are people used the syringe/remembered it's purpose seeing as that it was used so much during the games cutscenes - and that the whole story revolves around nanomachine control and that the Syringe's description says you can use it on other people for a non-lethal "throat jab" - and I tried to CQC vamp once and it didn't do anything special, so I just slit his throat and it killed him, and then he revived - that's when I called Otacon over and over. I'd say this one is a LOT more fair than Psycho Mantis was seeing as if that came to you without having to call the colonel then you are a frikin' puzzle game genius.

Must... not... mention... GLaDOS...

Good: Xemnas in KH2, not all that challenging but great effects.
Bad: Andross in Star Fox Adventures. Way too tacked-on.
Ugly: The final boss in Earthbound. 'Nuff said.

I read the manual to MGS4,it clearly states that triangle is to slit throats in CQC OR USE A PLUG OR SYRINGE IF ONE IS EQUIPPED.

ElArabDeMagnifico:

Ultrajoe:

I played for 2 hours before looking up how to drop this sucker. I know he's not the end boos but this deserves mention, he's not even hard to kill repeatedly, but after so much of the shooty i had to do some weird crap with the syringe?

i knew i had to use the syringe but i had no idea how to do it, i had never done it or even bothered to grab someone until that point, great fight but poor design. i would not have minded if i had done it in the past or had been told about it in passing to preserve the feeling of 'Well what do i do!?' but to me it reeked of the developers having more fun than me.

Pfft, you must not remember people getting pissed off about Psycho Mantis, and then got even more pissed off when they realized that all they had to do was call the colonel to figure out what to do (and he simply tells you "Plug the controller into Port 2". I killed that bastard twice in MGS4 and then just spammed with Otacon calls until he figured it out. At least with vamp, chances are people used the syringe/remembered it's purpose seeing as that it was used so much during the games cutscenes - and that the whole story revolves around nanomachine control and that the Syringe's description says you can use it on other people for a non-lethal "throat jab" - and I tried to CQC vamp once and it didn't do anything special, so I just slit his throat and it killed him, and then he revived - that's when I called Otacon over and over. I'd say this one is a LOT more fair than Psycho Mantis was seeing as if that came to you without having to call the colonel then you are a frikin' puzzle game genius.

I went through MGS4 without a strat on my first time through, as I do with all games. Even 2 hours into the Vamp fight, when I realized I called otacan and he said, his nanomachine's regenerate too fast snake! I realized, OMFG SYRINGE! And I had so much pride when I killed him on my own.

ElArabDeMagnifico:
I killed that bastard twice in MGS4 and then just spammed with Otacon calls until he figured it out.

Exactly what my brother did. Mind you my brother killed him ten times before contacting Otacon. Then he had read the instructions to figure out how to do it.
After hearing Vamp say "While the nanomachines flow through my body I cannot die" for the fifth time I tried to convince him that there must be some way to disable the nanomachines.

I told him to shoot the dolls away from Screaming Mantis' hands after he was about to throw in the towel, battling her for 5 minutes with no result.

Programmed_For_Damage:

ElArabDeMagnifico:
I killed that bastard twice in MGS4 and then just spammed with Otacon calls until he figured it out.

Exactly what my brother did. Mind you my brother killed him ten times before contacting Otacon. Then he had read the instructions to figure out how to do it.
After hearing Vamp say "While the nanomachines flow through my body I cannot die" for the fifth time I tried to convince him that there must be some way to disable the nanomachines.

I told him to shoot the dolls away from Screaming Mantis' hands after he was about to throw in the towel, battling her for 5 minutes with no result.

My friend was over there when I was fighting Mantis too, he said "Just shoot the fookin dalls BRO"

Best: Gannondorf in OoT, it was the most interesting boss i'd ever played and very original.

Worst: Guilty spark 343 in halo 3. Made me have the, "really, that's it?" moment. Luckily the racing part sorta made up for it.

Ugly:Freebird in GHII. Made me break my first controller

The good - Sonic adventure 1, fighting against perfect chaos. Even though it was pretty glitchy, i thought it was really fun playing as super sonic and beating it made you feel like you'd acheived somthing. (Dreamcast version).

The bad - Halo 3... 343 guiltyspark. I just found it utterly lame. I know everybody wanted to beat this guy up, that was cool. He just really didn't deserve a final boss role in my opinion. Fighting the gravemind and having to run up his arms and shoot him in the head would've been cool, whilst the ark explodes around you.

whelp, i guess that guy thought the same thing

Good- Dungeon Keeper ^^ Both the normal end dungeon and the Deeper dungeons. Every Deeper Dungeon was essentially a boss.

Bad- Black and White 2
ARRHRHRHR!!!!! The entire game is lame, but the ending level is just so fcking easy.

Pretty Sweet End Bosses: The End Boss of Viewtiful Joe, where the main difference is that you're now inside your giant robot and rival the size of the Earth itself. Pretty sweet.

Also, Jyggalg from the Shivering Isles, who is about five times your size and wields a rather large claymore like a dagger. Pretty sweet.

No shortage for Mehrunes Dagon hate here. I'd forth(?) that remark. He looked iffy, but was huge and menacing, but you didn't even get to fight the guy.

Good end boss would be The Master from Fallout. He made having a speech impedimat cool.

Good End Boss: Melbu Frahma from Legend of Dragoon.

I mean, although I didn't understand what was going on for half the battle, it was EXTREMELY epic. However, his 2nd and 5th forms annoyed me. (2 kept on firing clones of your characters at you, and 5 used the Dragon Staff, anyone who's played it knows how annoying that gets.)

For those who never experienced the above mentioned gem:
The Holy Vigoor Emperor from Ninja Gaiden would have to be my second favourite.
Although they didn't need to add the blue Murai guy at the end, I just felt that he was just an in-game story filler.

Bad End Boss: 343 Guilty Spark from Halo 3.

1) Car chase in the bowels of a spaceship?
Not a boss, but still awesome, especially when the theme plays in the background.

2) Overshielded and overpowered monkey with a hammer?
Fun, I'll have to admit. The atmosphere of rushing as Halo activates provides an awesome gaming experience.

3) Glowing Blue (Now Red) Floaty Ball Thing (343 Guilty Spark)?
No. I was really annoyed at this anticlimax (although the lead-up was exhilirating), not only because it was just a terrible ending, but because I bought the game expecting the final fight to be against the tentacled mass that is Gravemind (I was twitching to fire rockets and lob grenades into its mouth, a la Great Mighty Poo from "Conker's Bad Fur Day").
What I recieved was nothing short of a disappointment.
The final Warthog joyride through the collapsing Halo was pretty, although it was very ripped off the first game, and not anywhere near as fun.

juandonde:

Harleycosmo:
The bad - Halo 3... 343 guiltyspark. I just found it utterly lame. I know everybody wanted to beat this guy up, that was cool. He just really didn't deserve a final boss role in my opinion. Fighting the gravemind and having to run up his arms and shoot him in the head would've been cool, whilst the ark explodes around you.

BluHarvest:

Worst: Guilty spark 343 in halo 3. Made me have the, "really, that's it?" moment. Luckily the racing part sorta made up for it.

Wait a minute? You mean to tell me that the last part of Halo 3 is exactly the same as Halo 1!?

In short: Yes.

Good: The Transcendant One from Planescape Torment. Similar to the Master in Fallout in that you've a number of options as to how to defeat him, I personally prefer threatening to 'will' him out of existance and forcing a merger.

Bad: The big Antlions in Half-Life 2. Sure, the first few were pretty fun. But seriously...I'm gonna be really peeved if I see one in the next Episode!

Good End boss: The Cow in Postal 2! Seriously, one good boss that comes to mind is the one from PoP - Two Thrones. Lots of attacks, plus you need good skills to reach him at the end jumping from one rock to another without falling. The final blow is very well presented too.

Bad End boss: Strange noone mentioned Jericho. The Firstborn may look scary but once you figure out what to do to him its over in a matter of seconds... really dissapointing for a Clive Barker inspired game...

Good: Bohan, from Heavenly Sword. The music, the effects, the battle style, his epic transformation, and of course the amazing finisher sequence. Everything about that fight was sublime, even if it was too difficult for a lot of people's tastes.

Bad: Al Mualim, if there was one person in Assassin's Creed you could not throw down and stab, it should have been him.

Good end boss: Baldur's Gate's Sarevok.
Bad end boss: Nemesis in RE3. I hated RE3 in terms of storyline already. If the combat mechanics weren't broken, however, Nemesis may have been more of an experience.

And BTW: Dagoth Ur was at least a lot more interesting than the bosses in Oblivion.