I bought three games last year: Starcraft 2, Battlefield Bad Company 2/Vietnam and Call Of Duty Black Ops. All three games are very good and I am completely satisfied with my purchases.
I'd have to say, Starcraft 2 wins my vote though it's not the easiest game to get into and requires a hell lot of time to familiarize yourself with which is why I find myself playing Bad Company 2 the most these days as I'm on a tight schedule and I don't really have a lot of time to practice build orders and such. Starcraft 2 is meant to be played during long vacations. If all three games were given a substantial amount of time for familiarization (say, one whole month or more) then you will see that Starcraft 2 is actually the most consistent and most rewarding of the three games I mentioned hence why I say it's the best game of 2010 for me.