GTA IV by leaps, bounds and miles.
I enjoyed Lost Odyssey to an extent and while I consider myself a huge NG fan, I was let down by NG2. No game has kept my attention this year like GTA IV.
R6V2 was crap IMO. It was a bigger let down for me than NG2 was. Burnout was a pleasant surprise, but I got bored with it after about 2 weeks of solidly only playing that. Im still playing GTA IV. DMC4 was similar to Burnout, but I never got really deep into the older DMC games, so I beat it, grinded for a few achievements and traded it off.
Now Im excited for all the new sports games (NCAA, Madden to an extent, NHL, and FIFA), and of course the big holiday titles that dont need naming.
MGS4 is my G.O.Y right now though.