1. Fallout (3 and Vegas)
2. Skyrim
3. All 3 Mass Effects (I can't just play one without playing the other 2)

0_o

1) World of Warcraft - 1200+ Hours
2) Garrysmod - 1014 Hours
3) Team Fortress 2 - 511 Hours

I just can't commit myself to one game like others can. World of Warcraft was the only game EVER to keep my attention for almost a year straight.

1. World of Warcraft
2. Final Fantasy XIV
3. Final Fantasy X-2

Not counting pokemon, because otherwise this would be a very repetitive list...
1. Halo Reach
2. Halo 3
3. Smash Bros. Brawl

In a single playthrough?
1: Persona 4
2: Fallout 3
3: Okami

Otherwise?
1: Warcraft 3
2: City Of Heroes
3: Starcraft

Rome Total War
Gran Turismo 4/5
Mount&Blade/Warband

1.World of Warcraft
2.Mount and Blade Warband
3.Skyrim

I think

Oblivion, Mass Effect (also my character record with 13-14 characters made), and Halo: Reach.

1. The first Dawn of War games. Skirmish mode took all of my time.
2. Final Fantasy games. Lumped together because if I didn't, those 100's of hours per game would be first to thirteenth.
3. Guild Wars.

Skyrim's up there, with roughly 150 hours. Oblivion may be ahead of it, since I have played multiple files.
I maxed out the game clock in Jump Ultimate Stars, so I have no idea how long I've played that for, but it's at least 100 hours.

Finally, Kingdom Hearts II. I've beaten the game maybe four or five times, and that takes about 40-50 hours. Now, we add in my extended save file, which I've brought up to about 90 hours, and I'm not done with it yet. So that's what, ~300 hours? Not counting any potential save files where I hadn't finished.

Now, if we have an element of synonymity between 'games' and 'series of games,' then the order, from most to least hours, goes Kingdom Hearts by a ridiculously long shot, with Pokémon and Elder Scrolls locked in a heated battle for second place because I can't remember all the past save files I've had.

Team Fortress 2
Super Smash Bros Brawl
and Dissidia Final Fantasy

FF VII. I do not know how long, but I've managed to split Knights of the Round twice. Add the hours it took to find that thing and you do the math.

Plants Versus Zombies. I managed to level up the world tree to max height, now I have a million useless bucks.

Tekken series in general from 3 up. I'm killer with King and I can do all of his chain throws in battle against living people.

I can't give a specific order in how much I've played, but I can give the order in which they came out. They are as follows:
1) Morrowind
2) Oblivion
3) Skyrim

Oh I would have to say:

Streets of Rage 2- Still have my Megadrive copy & have it on XBLA though for some reason its stuck on trial version (anyone else have this problem?) Still playing it 20 years after it was released! Can anyone beat that?

Fallout 2- The best Fallout game in the series & still my favourite RPG of all time! Got it when it came out & im still playing it!

Suoer Smash Bros series- Me & my brother have played countless hours with each instalment! Everyone bring ing great joy & unprecidented levels of fun!

Heroes of Might & Magic 3 would be the closest runner up!

EDIT: Hmm it looks like you mean this generation! In that case, Fallout 3, Gears of War 2, and Dragon Age Origins!

1.Final Fantasy 7
2.Dragon Quest: Journey Of The Cursed King
3.Fallout 3

I would say Mass Effect and the original Contra are up there.

Currently, I have about 140 hours played on Borderlands since mid-February. It's quite addicting and I'm playing it on both Xbox 360 and Steam.

X-Com
WoW (Launch to beginning cata)
Civ 4

In that order

1. Pokemon Red...so much time...gone forever...the music still haunts me in my sleep.

2. Battlefield 1942

3. Legend of Zelda: Ocarina of Time

I just don't have the gamer stamina that I had a decade ago.

The time spent on the entire Mass Effect series probably beats Zelda, but I don't think a trilogy spread out over several years should count.

1) Star Wars Galaxies
2) Perfect Dark
3) Mario Kart 64

FFX and FFVIII come in pretty damn close too, but I've played the top three for an obscene amount of time.

Dragon age: Origins =150 hours
Fallout 3+New Vegas(I consider them equal)=400 hours
Oblivion= 450hours

1. Guild Wars
2. Oblivion
3. Skyrim

The old Republic will be taking over Skyrim soon... very soon.

Even though Fallout 3 isn't my favorite Fallout game or one of my favorite games of all time, it's a good game, and I did spend a lot of time on it. WoW is self-explanatory.
As for Doom, I still play it today in multiplayer over Skulltag. You probably guessed it from my avatar.

1) Fallout 3
2) World Of Warcraft
3) Doom 2

1) Majesty: A Fantasy Kingdom Sim
2) Age of Empires (entire series)
3) Knights of the Old Republic

Not going by specific clocking, but by how much I remember playing them.... the games I know I've played constantly.

In no real order.

*Fallout 2
I play the new ones as well but that game has served me well for years.

*Civilization (any)
Yeah more Civ 3-4 then I care to admit, and 5 is creeping up there in time played.

*Freelancer
This game STILL has active players, I can not stop playing it modded or otherwise.

1. Kingdom Hearts 2
2. Kingdom Hearts 1
3. other...

1) Fallout 3 (Every Quest Complete + multiple other play through)
2) Mass Effect 2 (Around 6 complete plays maybe more)
3) Dragon Age (Multiple plays)

If however we can include the entire series in the count it would be.

1) Fallout 1 2 3 NV (Complete plays on every one but 2)
2) ES Obliv and Skyrim ('nuff said)
3) Mass Effect 1 2 3 (Played ME1 MUCH less than the other two)

1) League of Legends - playing about three-four games a day at the height of the holidays. About 510 wins on Standard mode.
2) Dynasty Warriors 6 - Story Mode every character + every map on multiple difficulties.
3) Stronghold Crusader - All campaigns; games lasting several hours on many maps.

#1 would easily be Morrowind. I don't know how many hours, but I played it every day for a long, long time. Several hundred hours, I'm sure. #2 and #3 are harder to figure out.

#2 I'm thinking Goldeneye, because for a long time I only owned it and Mario Kart 64 for my N64 and I played the hell out of it.

#3 I'm thinking Raven Shield... I played a ton of its multiplayer back in the day.

ohh.. lets see...

Europa Universalis
Guild wars
Neverwinter nights 1 on a persistent server.. and 2 in general

1. Fallout 3-Lost pretty much a year to that game....Then the expansions came out.It was the atmosphere that drew me in.

2.Oblivion/Minecraft-I cannot remember exactly how much time I actually spent on Oblivion, but I remember a lot of early mornings and late nights.Minecraft...I am continuing to play.My brother and I recently set up a multiplayer server, and I have found the joy of friendly competition.

3.Stuff on gameboy.I can't recall how long, but I played Castlevania Aria of Sorrow and Pokemons for a long time.

1) Battlefront 2
2) Oblivion
3) Rome Total War

This would just be estimates, I played Battlefront 2 for about 3 years straight on Ps2, and my Steam says I have 200 hours on my PC version. Oblivion is around about 600 hours and I have no clue about Rome, I just know I've played it heaps