Interesting, although I just don't see how an FPS would be practical when played with Natal. Natal definitely has potential, but I seriously doubt it will be utilized for much other than generic shovelware(ex. 95% of the Wii library). Based on Microsoft's track record with this type of thing(Avatars), I'm still not on board with this one.
Regardless, Natal definitely looks like it could deliver some great experiences.