what game have you played the most?

[Reasonable]

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.