Here's a list of my favorite Wii games:

Game Genre Comment
Red Steel FPS great soundtrack, nice story; hate the swordfights though
Metroid Prime 3 FPS nice graphics
Onslaught (WiiWare) FPS lots of fun playing this plain and straight forward shooter
World of Goo (WiiWare) Puzzle very addictive
Okami Adventure really great graphics, nice gameplay
NfS: Undercover Racing made a lot of fun playing it with the GC controller