Project Gotham Racing 4 and Forza Horizon.

Trials Evolution, Minecraft, The Witcher 2

Dark Void is a great game you can get for 7$ used. It's boring at first then you start getting different types of jetpacks and it becomes awesome. :P

I played Alan Wake PC version, great game. You should check that out.

aside from the ones Darnasian mentioned, Dead Rising 1 and 2 are also pretty cool, if you're into the horror genre

And... Darnasian pretty much said all the 360 exclusives hahaha. Go with what he said :P. 

Oh and if you're into RPGs you could also check out Tales of Vesperia, Lost Odyssey, and the Fable series :D

Uhm...all that comes to mind are Halo , Gears of War and Alan Wake. Ninety Nine Nights is worthwhile though you may not like it and Crackdown is meh. Left 4 Dead is also great. Splinter Cell Conviction should work too. But aside from that , Xbox sucks in the exclusives department and we all know that the exclusives are the feats that matter to a console , the games that other people can't play , so not much enjoyment here.