Internet Kraken said:
Super Mario Galaxy. Probably the most time I've spent on my Wii besides playing the virtual console and some Game cube games.
It sounds like you want some recommendations for good Wii games. If that's the case, then you should tell us more about your gaming preferences.
I agree. Super Mario Galaxy not only will take a fairly decent amount of time, but it was great fun for me.
Some other good games:
The Conduit (Sci-fi FPS)
Madworld (Don't have it, but heard it is good)
Mario Kart Wii (Racing game, fun with friends)
Wii Sports Resort (Expansion to Wii sports. Adds new games and great with friends or family.)
Legend of Zelda: Twilight Princess (A good Zelda game. Took me a while to beat, and I enjoyed it immensely)
Fire Emblem: Path of Radiance (Strategy game with some RPG elements, if you liked the other ones, you will like this.)
No More Heroes (Great action game. Lots of fun)
There are some others, but these are the most prominent, and the ones I enjoy the most.