Since I base my selection on how addictive the game was:
Console- Blazblue Continuum Shift. I enjoy fighting games, and ARC systems know how to make kick ass fighting games that are addictive as hell. And I'll keep on playing it until I get a new Guitly Gear...if that ever happens.
Runner up I guess would be ME2. Was pretty decent and while not as amazing as people claimed it to be, it made improvements to the game that pleased me...even if the story was a little spotty. I have a real tough love relationship with ME, they are average at best games, and I despise them on some level...but at the same time I still play them because of my inner sci fi geek craving a sci fi RPG and there are a few redeeming qualities I guess.
Portable- Peace walker for the time being, excellent game with tight controls, gameplay, and awesome story. It looked, sounded, and played great and had a ton of content, really outdid itself.
Runner up would be Birth By Sleep. All I have to say it Bravo squenix, it was my first KH game and it left a good impression on me and enjoyed it quite a bit. Turned a non fan into someone who will pursue playing the others some day.
Although God of War: Ghost of Sparta comes out next month and it's looking awesome based on the hype and the demo I played. It would very well steal GOTY portable for me if it's anywhere as good as Chains of Olympus...which it looks to be that way.
All I know for sure is that Dissidia 2 is automatically my 2011 GOTY, unless they fuck up huge in some way....which I don't see happening. March/April can't come sooner.