Shadow Complex was a 2009 2.5D Metroidvania exclusive to Xbox 360. It attracted quite good reviews at the time, and is widely considered among the best digital-only games available for the console. It won't be exclusive for long though, because a recent PEGI listing indicates that a remastered version is coming to PC.
That's not an official announcement, but ratings boards generally don't rate games that don't exist, so I wouldn't be surprised if we hear more about it in the coming weeks. The game is based on Orson Scott Card's novel Empire, and as the trailer below will indicate, it looks pretty good even without a remaster.