There are a lot of problems with Wii Music. The first is that they ignored traditional gamers. They should have put more depth in the game so that traditional gamers would feel like 50$ is worth that game. Adding a Mario Paint like music creator would have been a great idea. Mario Paint songs are extremely popular on youtube and Wii Music could have used that. That would have brought a lot of free advertisement and replay value to the game. Nintendo doesn't realize it but traditional gamers are those giving positive word of mouth about the Wii. They are also those that make the expanded audience try the game. Most people have tried Wii Sports before buying a Wii.
The second big mistake they made goes with what the OP is saying. That game is more representative of playing music than GH and RB. Playing music in a band is hard and require a lot of practice. When you play RB, you don't really need practice because you either miss the note or play the note. That way, your timing is always perfect and even if you completely screw up, that won't affect the way the song sounds. In Wii music, you really need to be tight or it really sounds bad and that require practice. At E3, they should have practiced a lot more or called actual musicians on stage because the way they did it, it sounded like a really bad garage band.
How many cups of darkness have I drank over the years? Even I don't know...
