In my opinion the one game that is worthy (no offence to the others) is Skyrim - people had high expectations for it, and it didn't disappoint most of them as the Internet shows. Free world, fun, addictive etc.
If I had to choose 2nd and 3rd, though, I'd say Portal 2 is almost on par with Skyrim (I know it even without actually playing
) and the third place would go to either Crysis 2, Battlefield 3 (due to it's pre-release popularity) or Deus Ex: HR (my own opinion). Also, I didn't give a place to Minecraft, because actually it has been out for a while now (not just 2011) - a worthy game for the competition though.