I read a lot here and on the internet, and I often see Wii Music listed as one of the worst games put out by Nintendo.
I got it about a week ago, and I'm having a blast with it. It's not Guitar Hero or Rock Band (both of which I have and play a lot) but it was never meant to be. It's something different... rather than imitate what you see on the screen, the game encourages you to play around and make each song into something different. What it sets out to do, it does very well.
Sure their are problems. Some of the instruments don't sound as good as they could, among other things. But there's something about taking Twinkle, Twinkle Little Star and making a punk version out it that I find quite fun and satisfying.
I'm not saying it's for everybody. I'm just saying I think it's a very good game and not an embarrassment for Nintendo and surely not shovelware.