Well, it's probably WoW.

I've got about 130 hours on San Andreas for the 2 100% saves played through (and then random stuff in the city for dayyys).

Just checked my Pokemon Crystal game too (it's dusty  ) and it had about 130 hours.

World of warcraft. I spent over 5,000 hours on it.

Final Fantasy IX, pure unlimited fun.

This is a hard one... When I was a kid, Golden Axe for PC. Later, Warcraft II, Starcraft and Quake. Nowadays, Ninja Gaiden Black and Mario Kart Wii.

Not including MMOs (they cheat) it would have to be Castle of the Winds I think. Or perhaps the original Civilization.

Diablo 2, hands down. Second place goes to Diablo/Hellfire and the Heroes of Might & Magic series.

Super Mario Kart (SNES), no doubt. I played and I'm still playing this game a lot.

Super Smash Bros. Melee is definitely most played. I estimate 400-500 hours have been put into that game (and I have vowed to break this record with SSBB within a year). It's followed by Tales of Symphonia (5 full playthroughs, at least 200 hours), Super Mario 64 (don't have a time, but I played it a LOT), RE4 (about 4 playthroughs plus all the extras), Jazz Jackrabbit 2 (speed runs and normal runs, at least 50 times), Zelda the Wind Waker and Timesplitters Future Perfect (countless multiplayer rounds and arcade league matches).

Good question. I think I put plenty of time into these MMO's over around 12 months but that might just have been the pain of gridning...

WOW and EVE

I've played a lot of Day of Defeat online plus Quake and Unreal Tournament.

For SP it would be Oblivion I think - damn thing eats time if you really go for all quests with the GOTY edition.

I did play through Deus Ex five times just because I was so impressed with it and that took some time.

 You sir, spent almost an entire year of time on a game.  Is the flesh on your ass rotting off or anything?  Seems there would be some unwanted side effects to spending 200 days n a game world. 

I would say I have spent the most time playing Halo 2.

 Here are my Halo 2 stats.  If you were to say about 5 minutes a game that would come out to about 270 hours.  That is only a guess because matches can last up to 15 minutes or can last only 1 minute.  I would say playing TF on Quake would probably overtake it but I can't be for sure.  That was years ago.

• Total Kills: 40469
• Total Assists: 9744