Counter-Strike can't stop playing it..

Dungeons of Dredmor and Spelunky

The Movies, Mafia, Half Life 2, Monkey Island, and of course most of the Telltale episodic games.

Fable: The Lost Chapters, Diablo 2, Starcraft + Broodwars, Castle Crashers, Final Fantasy Tactics, Demon Souls, Dark Souls, Cave Story, Emperor: Rise of the Middle Kingdom, Age of Empires + Expansion, Rise of Nations, and etc.

I normally play a lot of sandbox-genre games, so I can't really say I've played it till the end...since the game never ends, haha. Unless, of course, we count the part where I screw up somewhere and get the game over screen.

The first time I played:
Dragon Age Origins, Dragon Age 2, Mass Effect 2 and 3, The Witcher, Assassins Creed 2 and Brotherhood and Revelations

Mass Effect series, went through all 3 in about 2 weeks. Would go to work, come home and play for 6-8 hours, sleep and repeat. Easily my favorite games ever, about to start a new character. :)

i played the sims 1 a lot :D

I still play Age of Mythology and Rise of Nations, almost 10 years later. -_-

Nine Hours Nine Persons Nine Doors...

Any Half-Life, Deus Ex 1 and 3, Arx Fatalis, Morrowind, Neverwinter Nights 1 and 2, Heroes of Might & Magic (old ones), Command & Conquer (old ones, but my favourite is Generals), any Devil May Cry, SH & RE (old ones), any Soul Calibur, any Tekken, any Red alert, Socom on PS2, any Fallout, almost any FF, Operation Flashpoint, Skies of Arcadia, NOLF, Hearts of Iron, any Ratchet & Clank or Crash Bandicoot, any Tom Clancy's series games (Splinter Cell, Rainbow Six, etc), any Red Faction except Armageddon, any MGS.... heck, this old stuff is cool!!!! No DLC rip-off, no DRM bullshit... sheer perfection!!! Modern games that can match up to this level are damn rare.

GTA Series

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Quake Live

Metal Gear solid, the first one for Playstation.

Heroes of Newerth and Dota 2

One of the best RPGs - Gothic 1 and 2 .

Arma 2 w/ ACE mod - 500+ hours and counting.

Tales of Vesperia. Even if I won it 3 times I still can't stop playing for hours and hours straight.
Borderlands :Q_.
And last, if I can count it, Super Smash Bros Brawl, when I got it the first day I played 26 hours straight, stopped because I had to see my cousin XD.

Left4Dead and Killing Floor and DOTA !

Grand Theft Auto, and I think that's the only one as far as I remember. I passed out once after two days without sleeping and fell asleep on my keyboard.

Halo 1-3, GoW 1-3, Halflife 2, Borderlands 2, Diablo 2, Diablo 3, Mass Effect 2, BFBC2, Bioshock 1, MW3, Crysis 2, Dead Island, F.E.A.R. 3, Section 8 Prejudice, UT3, There are some others, but not off the top of my head.

Diablo 2 and 3 weren't all difficulties in 1 sitting. Dragon Age Origin was close.

Tetris

fallout 2 and morrowind when i was a kid. now there is no such a game

Dark Souls: Prepare To Die Edition

Finally caved in after a few months and have been enjoying it ever since. One of my favourite games already.

Peggle what a perfect and addictive game...