There were some fairly decent games this year, as well as some...well...less than decent games.
If I had to pick a top five, it'd likely go as follows:
1: Portal 2 - Far and away my favorite game from 2011. And frankly, quite possibly Valves best game to date.
2: Rayman Origins - Despite my disdain for Ubisoft at this point, this was still a fantastic action adventure side-scroller
3: Batman Arkham City - Unsurprisingly, Rocksteady nailed this one. Better than the first, of which I loved greatly
4: Deus EX: Human Revolution - It had it's flaws, but it was still a fantastic bit of cyber-punk sci-fi gaming.
5: Battlefield 3 - I know, I know. "Just another modern military shooter", you're saying. And I agree. Plus, the campaign wasn't very stellar. Still, the multi-player is so fantastic I can forgive those grievances.
Honorable mentions:
WH40K: Spacemarine for making me interested in 3rd person shooters again and providing a FAR more cathartic experience than I ever had with Gears of War.
Fusion: Genesis for being, effectively, a more expansive, top-down version of Freelancer on the Xbox Live Arcade. Seriously, check it out.
Dead Space 2. The multi-player was annoying and pointless but the campaign was fantastic (mostly) throughout. These games continue to be among some of the few decent survival-horror series.