OK this one is a bit vague, but the question is: What were some interactive "scenes" in a game that left you completely floored at how well it was executed and crafted in terms of visuals, audio, and plain old magic? By "scene" I mean things like scripted sequences, boss fights, a part of a level, whatever. Anything that really left you thinking, "Wow - there must've been a lotta careful work that went into that part I just experienced." And I don't mean non-interactive cutscenes - but fully interactive sequences that look, sound, and feel absolutely spectacular. Maybe some examples would help clarify what I'm trying to get at:

God of War I - Hydra Boss Battle. The motion blur, rain effects, screaming sounds, and the way the hydras moved all came together to form one of the most awesome boss fights ever - and you get to experience it within 30 min of the game!

Snake Eater - Final Boss Battle. All I have to say is: the flowers. Top notch art direction and an impressive technical achievement on the PS2.

Shadow of the Colossus - "Vacuum" Ending. Hopelessness embodied in a simple yet profound interactive sequence.

Portal - Furnace Escape. The music kicks in just at the right time to give you that adrenaline rush, putting into motion one of the coolest end-games I've ever experienced.

Call of Duty - Reichstag Rooftop. Taking a page right out of the history books, you're treated to a virtual re-enactment of one of the most recognizable photos from WWII, with grand orchestral music and all. (I really need to play COD4).

I Have no Mouth... where each of the five characters losing has the same fate but explain it in an entirely different way.

The multi-level fight against the turrets in Portal
taking on the striders in HL2E2

this is hard. I most love the sequences where it feels like you just made it by the skin of your teeth, but there are some games where that's all it is. Stranglehold, for example.

The "Final battle" in Oblivion... yeah, you all know what I'm talking about. With a little tweaking of the game's music files, that whole part was incredibly epic.

Half-Life. All of it.

Curst in Carceri, in Planescape: Torment. Running around desperately doing good deeds while the city went into seizures of violence all around me was absolutely exhilarating. Demons sprung in out of nowhere, chewing up panicking townspeople and errant party members; asshole wizards stood on inaccessible ledges lobbing burning pain into the frothing crowds; two fucktastically powerful archdemons tore chunks out of each other while easily flicking away any pansy attack I tried to poke them with, and in the middle of this here I am, trying to convince everyone to just calm down, band together, stop stabbing each other in the back and make some sense out of this disaster. Tres fun.

The final Strider battle in HL2EP2 was really neat because I fought as hard and quick as I could and made it just in time. Very well designed.

In the first Call of Duty, the whole first mission of Stalingrad. You're on a boat crossing the Volga, planes fly by, shooting and blowing up the boats around you. A few comrades attempt to abandon the boat only to be shot by fellow Russians. When you finally get to the other side, your boat is blown up, then you have to stuggle up the hill facing machine-gun fire and working with a sniper to avoid getting killed. Very epic.

CoD4 was awesome but, something tells me you'll still appreciate the first CoD's (and UO) a little more, even though the last one is pretty cool. I want to add "Hill 400" from CoD2 to that list, and the Russian Campaign in CoD2 also had some amazing parts, like imploding the building.

Lvl 64 Klutz:
The "Final battle" in Oblivion... yeah, you all know what I'm talking about. With a little tweaking of the game's music files, that whole part was incredibly epic.

Not sure if this is what you mean, but playing FF8, fairly near the beginning is a big battle, and you get chased by a mechanical thing (spider? I don't know, it was years ago and I never played much of the game). As you run for the beach(?) it switches in to a cut scene, and then all of a sudden you realise that you are still in control of your character. By modern standards it's nothing, but at the time I was just gob-smacked.

Another vote for Shadow of The Colossus as well. Oh and for the first Russian level in Cod - the bit where you stand in line and they give the bloke in front of you a rifle but you only get a clip was "WTF!" all over.

Any "R1 Views" in Snake Eater are awesome. Particularly at the end of the Virtuous Mission where

Awesomesauce.

I have to agree with the end of HL2 ep2.

It was so tence I had to play it in two parts to avoid overheading myself. By the end of it I had bit all the skin off my lip. So so so so good =D

The Bioschock plot twist.

Quake 4: The being turned into a scrogg scene. You travel along the conveyor belt, unable to move but still watch the scenes unfolding around you. The addition of another capturee only meters ahead of you going through the scroggification, screaming in pain as you can only watch adds to the horror. Then it's your turn and the saws come down...

Oh, I know I'm going to get crap for this, but I'm going to have to say Shenmue.

Yes, I said Shenmue.

There are lots of those action interactive scenes depicting normal actions and I think that they execute pretty well. Sure, they bleed cheese but I always enjoyed playing those.

I would differentiate boss fights from interactive scenes myself, but if they're the same I have to pick FFX's last couple fights.

Fahrenheit (or indigo prophecy), despite being Queen of roller-coaster, crappy, pointless plot twists 2/3s through, surely deserves a mention here?

Fahrenheit's scenes worked best when you were under pressure, and didn't really get to think about choices. Most conversations were like that, because of the time limit, and so came across as more script-like. It flowed much better. The (albeit brief) moments where the kid slips in the lake and when the police are making their way to the old woman's house stick in my mind.

fsanch:
Oh, I know I'm going to get crap for this, but I'm going to have to say Shenmue.

Yes, and crap will given: WTF ARE YOU THINKING!??!?! :P

Another old school one: Doom 1 - Phobos Anomaly. That music...jesus christ! And when the 2 barons first come out, with that demonic scream, and you realize you're walking on a pentagram and stuff...plain old awesome. The cyberdemon battle was pretty sweet too. You knew something bad was coming when you got fully stocked with ammo.

Bakahead, it's "Strogg", just FYI.

I like the "Coup" and "Aftermath" scenes in CoD4, but for me the real standout moment in terms of interactive set-pieces is probably Dark Messiah: Might and Magic.

Unfortunately, it's a spoiler of epic proportions. ye have been warned.

I often load up Prey just to experience the first five minutes, truly epic.

Don't fear the reaper.

Iron_will:
The Bioschock plot twist.

I hope you are talking about the golf club scene, because the actual plot twist itself was something I'd expect in some kind of B grade movie trying to have a good story by having those

endings.

fsanch:
Oh, I know I'm going to get crap for this, but I'm going to have to say Shenmue.

Yes, I said Shenmue.

There are lots of those action interactive scenes depicting normal actions and I think that they execute pretty well. Sure, they bleed cheese but I always enjoyed playing those.

You won't get any crap from me; I totally agree with you.

Man_In_Gauze:
Half-Life. All of it.

Wow like that isn't completely one sided.

My favorite is the Zakhaev assassination attempt fromm CoD4. Just the sound of the .50 cal sends the adrenaline rush you need... Then seeing the hotel explode seconds after you escape...

Phoenix Wright is basically an interactive book.

While on Assassinations, the Assassin's Creed assassinations are pretty amazing.

The "credits" assassination scene in CoD4. You actually felt like you were being held hostage and the only thing you could do was helplessly watch the myriad of things going on around you. And the end with the gun being levelled at your head, with the controller throbbing along to the heartbeat. It is totally engrossing!