Mine is Destroy All Humans 2
From 2000 to 2010?
Probably the original Halo. In fact, almost certainly the original Halo.
Then, maybe Portal. Mass Effect 2 is a close third. Then the Half-Life 2 games (original and episodes all together). Project Gotham Racing 3 is up there on my list, too.
SOOOOOO many choices. Cannot deciiiiiiiiiiiiiiiiiiiiiiide.
I've got fond memories of the MGS games, Gitaroo Man, Prince of Persia: Sands of Time, Metroid Prime / Fusion, etc.
I'll agree with GE. SSF4 has reignited my love for fighters like no other game before. Never before have I cared so much about improving my game.