The game that you could never put down

Self-explanatory title.  What's the video game that you played for the first time and you could never put it down since then?
It's alright if you have more than one.

Mine would be Gears of War.  Ever since I got the game on Emergence Day I haven't stopped playing the game since and it's been almost 2 years.  I did play games in between, but always kept playing Gears.

to this day i still play Tetris DS to hell.  same with DJ Max Portable 1 and 2.

Guild Wars. 700 hours and counting.

Tetris DS
WoW back when I played
Metal Gear Solid 2

Shenmue and Vampire Bloodlines. I find myself re-installing it a lot of times.

For single player, probably Final Fantasy X. I remember playing that non-stop when it first came out.

For online, WoW. Though I quit a year and a half ago.

ocarina of time XD

My friend can't put Tetris DS down either.

Day of Defeat: Source WAS that game, but I've put it down now

oblivion

Civ serise. Get up in the morning. Switch on PC. Play Civ. Go to bed.

Mine is Final Fantasy X as well.. I beat the game twice, one file currently has some 125 hours on it. And then I went and bought Final Fantasy X: International, only when I tried modding my PS2, it didn't work as advertised, so I basically had to sit on the game for quite a few years for PS2 emulation to catch up, and now I'm finally getting to play it on my laptop and/or this PC.

I suppose I keep going back to TF2, although that's a fairly new game. And CS:S. Good times to be had there. Recently gone on a Supreme Commander binge though.

God Of  War and Crysis..

MGS4, FF9, FF7

gta,FIFA-the all time great,call of duty all games

Knights of the Old Republic, FFVI, Oblivion, Mass Effect.

Metroid Prime, Zelda OOT, Final Fantasy IV, Super Metroid, Shadow of the Colossus.

Call of Duty, played way to much online back then.

Roblox

WoW and MGS3

WoW

Picross DS, Puzzle Quest, and FFXI.

X-Wing
Tie Fighter
Sim City 2000
StarCraft
ActRaiser

A game that I played in almost one sitting was MGS4. I played it for hours at a time and love every minute of it.

A game that I keep coming back to is Geometry Wars: Retro Evolved on XBLA. I suck at it, though.

Mercenaries

I beat Resident evil 4 at least 5 times in a row. It's a real laugh riot when you get the Chicago Typewriter.

For a long time Guild Wars: I have over 2000 hours, not something i'm proud of. Right now Cod 4 multiplayer. I keep going back to it.

Football Manager 2007 for PC.

Metal Gear Solid 2
God of War
Halo :CE

Grand Theft Auto IV for 360
Burnout Paradise for 360
Dragonball Z Budokai Tenkaichi for Wii

Orange Box, I love playing Portal and HL2.  It stays in my gaming diet pretty constantly.  Also, Symphony of the Night, which I love playing so much that I actually purchased it from both the PSN and XBLM.  So that no matter what system I'm playing, I have it at my finger tips.

Halo 2, If I put all the hours I played of Halo 2 together it would add up to 42 days straight.

Probably would have to be Metal gear solid 4

Mech commander still playing it and it has been out for 10 years lol.

"Probably would have to be Metal gear solid 4
"

Project Gotham Racing 2
Tetris for Game Boy
Halo
Call of Duty 4

Runescape (embarrassing right?) and also Halo 2

The legend of Zelda: Majora's Mask, Half-Life 2, F.E.A.R., Call of Duty 4

Gears of War for me as well. The multiplayer is a blast to play with friends.

I've put a ton of hours into the Osu! Tatakae! Ouendan! games and Elite Beat Agents on the Nintendo DS, the difficulty curve on those games is perfect and a play through normal and hard mode will probably take at least 10 hours. I've actually had EBA shipped to me twice at college because every time I think I'm finally done playing that game, a few days later I'll have another craving to play it. Now Nintendo needs to listen to the "To Be Continued..." line at the end of Agents and give the US a sequel.

Unreal Tournament 1.

There are a couple of games for me: Civilization IV, Unreal Tournament 2004 and DJ Max Portable 2.

Pokemon, I wasted probably 3 straight summers playing those games non stop with a buddy.

Tetris. Leave me with my Tetris!

Either Super Mario World 2: Yoshi's Island or 007 Goldeneye.

My friend and I used to play Halo: CE for hours on system link, summer after it came out we were playing 4-6 hours a day.

You know I honestly can't think of one. I guess I just get everything need out of a game and then forget about it.

Football Manager 2008 (and the previous iterations). I probably have spent over 400 hours with FM208 alone.

Counter-Strike: Source

The game is strangely compelling. Still go back to it for my cs fix every once in awhile.

When I first got Assassin's Creed I was so addicted to it, I wouldn't prize my hands off of it for anything. Granted I hardly ever play it now, but those first couple of days I got the game were like one non-stop gaming binge. But one that's kept me coming back even so long after it's release? Okami and Shadow of the Colossus.