Natal is an interesting and novel approach. I think its got three key markets.
1. Interface for computer/media playback.
2. Game interface.
3. Communications interface.
It doesn't need to be great at all things for every person and it can be good for more than one market area at the same time, i.e. games + communications or media or all three.
Someone who wants it for an interface/webcam/communicator on the PC may find its a pretty good webcam with an excellent mic and great night vision capabilities.
Someone who buys it for the Xbox 360 may easily use it for movie/music playback as well as getting rid of a headset because the array mic is pretty good for noise cancelation and may never even play a game with it. Netflix is as important as any one game on the Xbox 360, so the utility of this device doesn't begin and end with games.
This interface isn't just going to be proving itself as a games interface its going to be proving itself as a concept for a human interface. The real potential of this device is in overlaying a haptic style (mass effect for example) interface into the field of view of a person using either 3D glasses or a display mounted to the inside of glasses. The present potential is limited to interaction based off of a 2D screen.
The best part of this technology is that it captures the parts of the market which the Wii hasn't been able to tap and even if the Wii gets replaced with a significantly faster model it still probably won't tap into the potential markets for Natal. So whilst Sony is trying to compete with the hellishly good Nintendo on their home turf, Microsoft has so many potential uses for this technology and so many partners they can tap into. Its really between Microsoft and the market here because theres nothing limiting the potential of Natal aside from themselves.
Do you know what its like to live on the far side of Uranus?