Mass Effect 2 easily. One of the best blockbuster games this gen. The sequel comes out this March, and you'll be able to import all of your decisions and data from ME2 into 3 (as long as you buy 3 on the same system). All-star cast, huge environments, great 'Dirty Dozen meets the Great Escape' story, and it's beautiful to look at.
*Plus* if you have a 360 or capable PC, pick up the first Mass Effect, and start from the beginning, as your decisions in 1 will carry over to 2 and 3.
Crysis 2 is good, but it's not ME2 good.