The number 1 game in 2011.

[okr]

Na, the best selling exclusive this year will be Pokemon Black/White. According to TheSource's article it already sold 6.49 million in the first half of 2011.

If you just meant 360 exclusives, the Halo 1 remake will have to compete with Kinect adventures which is at 3 million after the first half of the year.