I had a chance to play with the Microsoft XBox 360 Kinect motion system while visiting a friend in Seattle during PAX last week.
I was very impressed by the experience. There's no controller. None. Just you, your face, your hands, your body. You can interact with the system in a lot of ways - in Kinect Adventures, for instance, we played Dodge Ball. Rather than stop the ball with our hands, we were encouraged to use any part of our body that could connect with the balls hurtled towards us. It was a LOT of fun.
My main concern is with the Dance Central dancing game and its "feature" of showing you how your body looks in this weird trippy dance background thing. Not too flattering. My hope is that the Microsoft teams recognize that people (i.e. some women I know!) won't want to see their blobby figure moving about a spaced-out background, and allow you to disable this feature if you wish!
Anyway, I had a blast with it, and can see playing either alone or in a group. I'm definitely getting a Kinect for Christmas!