I was fairly unimpressed with both, though slightly more with Natal due to the lack of a live demonstration and the disclaimer in their advertising basically stating that you can't do as much as they say you can. Motion control [bold]can[/bold] be gimmicky but it can also be a great way of playing I think, the only problem is that nobody has got the right combination so far to make it a real staple of gaming.
In my oppinion, this is one step closer to the dream of literally being [bold]inside[/bold] the game, holodeck style, which is something I've been excited about for years. Sony is essentially giving you a reduced mo-cap suit and Microsoft is giving you a motion sensing camera. The only problem with Microsoft's Natal, I think at least, is the lack of something solid. In a game, If my character is holding something and I'm just pretending to, I think it would be a strange sensation. And it would be difficult to use a controller and jump around like an idiot at the same time anyway. At least Sony have given you the feeling of something real.
It's also going to cause more problems with exclusive titles, which I hate. It sucks that I have to own a specific console to get a specific game, especially when they're not exactly cheap. And now, developers either have to take the time to create the same game for both systems, pick one and make the game exclusive or just not make it for either system, which seems more likely.
Both are fairly unimpressive at this point, but it's hard to judge sans experience so for now I'll keep my mind open and give my final judgement when I've played an intense FPS with both systems.