The new Donkey Kong Country looks quite good. Will probably pick it up when it's $5 or so. Since not a single member of Rare did anything on the game, there's a good chance it's just a high quality 2D platformer -- one of my favorite genres (and the main reason to get a Wii: all the great 2D platformers on WiiWare).
I've been playing
TWINKLE STAR SPRITES
It's a competetive shooter/puzzler.
and
Time Bokan Series: Bokandesuyo