Super Mario Galaxy is amazing, but it will seriously mess with your head for a while.
Metroid Prime 3 is alright, I don't get why everyone was comparing it to Halo, it seems just like the first two games to me (though a bit better than the second).
I've also got House of the Dead 2/3, I really like lightgun games.
Didn't care for Twilight Princess, faaaaar too much bloom, and the Wiimote controls result in you just flicking your wrist around instead of pressing a button. I'd rather just play the GameCube version.
Plenty of other games I'd like to try, though...and of course, there's lots of cross-platform games for it. Lately I've been playing Guitar Hero: Aerosmith.
_________________
I'll brave the storm to come, for it surely looks like rain...