Natal has potential to be awesome, just as the Wii does.
It will be up to how the technology is treated. Nintendo have done well with the Wii, the reason people ***** about it is because of the crap everyone else releases, you can't expect one company to develop the console as well as fill its library single handedly.
Microsoft probably won't have that problem. Its already established itself as a console aimed at teens to adults, so it likely will dodge the multiple bullets that are shovelware games.
Unfortunately the Wii's cheap price coupled with its ease of use coming from the motion controls attracted games that wanted to take advantage of Nintendo's kid friendly attitude. Microsoft's issue will be attracting designers to design for Natal, I'd be surprised if it wasn't rather difficult to grasp (at least initially) so whilst I'm sure MS will make some awesome games for it, others might just stick to the basic control schemes.
Sorry if this wasn't as fluent and comprehensible as it could be, I'm not 100% with it atm.