Fun to play, horrible to look at...
Music
As expected from a GH game, the soundtrack is great. Although it's noticeably missing legends like Jimi Hendrix, it's still got a great soundtrack. Although the first venue's songs aren't very good, it improves very quickly.
Gameplay
Although arguably, the gameplay hasn't changed, tappable notes are much more noticeable. Star power now drowns out all other parts of the song (vocals, drums, bass) so you can appreciate your own playing. Or not.
Online Play
Nintendo finally has a game with a decent online system. You can go on Nintendo WFC and play against friends, strangers, and get a code to put on the GH website and eventually join tournaments. You can even invite friends to join games you're hosting. Although there are a few glitches, overall it's a welcome addition.
Graphics
Now, the PS3 and 360 graphics have been seriously praised. However, if you looked at the Wii version, you wouldn't be able to tell it was on Wii. You might think Dreamcast, but even that has better graphics. The graphics are seriously awful, and character movements look very robotic. The Guitar Hero 1 graphics on the PS2 are better than this. Good job Neversoft.
Overall, the game hasn't changed much from it's predecessors, which isn't a bad thing. However, the inexcusably bad graphics weigh this game down. Fun to play with a friend, but unfortunately, seperate guitars won't come 'till February.