I agree that XIII-2 has a lot of good music, but seeing as it was released in 2012, it'll be going up against Mass Effect 3 in my books. It'll be a FANTASTIC showdown!
Now, uh, what the devil happened in 2011, again? Hm... Not knowing many current games, I'll say Witcher 2. XIII-2 isn't half bad, but W2's music is about as good as Mass Effect 2! (... Hope ME2 is from 2010.)

(Though DCS A-10 has to have some recognition for the novelty of a flight sim with nice music... right?)