I never had too great expectations, and won't before they show some more software.
I expect it to do well with simple games, and in the fitness genre. I also expect that a few more complicated games will use Natal a bit (though in many cases it will be just to add a few gimmicks to the game).
It's hard to be disappointed with expectations like this. Anything more than this will be a bonus.
My Mario Kart Wii friend code: 2707-1866-0957