Natal has some very interesting possibilities, but it really remains to be seen how it turns out. Unlike the Wii, the 360 actually has the hardware to do immersive AI/physics/etc. along with the whole motion sensing thing. How any of this will turn out is really up to the inventiveness of the game developers, however, so I honestly doubt we'll see more than a handful of games outside of the wii sports ripoffs (which will be fun, mind you) that are actually any good. That being said, those few games could really bring things up a notch.
My only real gripe is that I would have to clear out a space in my living room to really get into motion games. That would be annoying.
~Jason