A lot of the games mentioned are cross platform, and the OP doesn't specify, so I'm not sure if this was supposed to be restricted to PC games only or not.
I understand it, because it's in the PC Gaming section, as "What was your #1 rated (PC) game of 2010", with the (PC) part being implied.
For me, it's a tie for the number 1 position:
Mass Effect 2/Dragon Age: Origins
Honerable Mention is easily Batman: Arkham Asylum, but it could've gone to Mafia II also.
Worst game of 2010 is probably BlOps. It's so bad, I wouldn't even pirate it!D:
(Fallout: New Vegas can be my game of 2011... but only because I just got it last week)