There are plenty of great Xbox games. My favorite would be a collection of Alan Wake, Mass Effect, Mass Effect 2… and Deadly Premonition. Wow, on second thought there aren't that many great Xbox games. However, I do believe it's worth owning an Xbox 360 just to play Alan Wake, Deadly Premonition (Although the game is planned to be localized to the U.S. on the Playstation 3 soon) Mass Effect and Mass Effect 2… However this does make me question my subscription to Xbox Live.
Alan Wake is really the only survival horror game left, and features one of the best narratives ever in a video game. And it is amazing it can hold the title of best survival horror game when it is rated Teen has no blood in the entire game. Unfortunately they kept it Teen to appeal to a bigger market and it didn't sell anyway.