What game of 2011 do you see yourself replaying again and again every couple of years, because you remember it very fondly?
Mine is Warhammer 40k : Space Marine. There isn't much to it, but what's there - slaying Orks by the score with a chainsaw sword and a bolter - well, it excells at it so much, that it's as satisfying and fun to do, as it sounds on paper. Love it!
That footage is from the demo. There isn't much more to the game than there is in the demo, but damn is it good! If you haven't gotten the game yet, do yourself the favor and at least play the demo. Over and over again.