I'll have to rent this game and really see for myself but so far this thread only strengthens my argument that it's great for the musically inclined like MaxwellGT2000 and a noise maker for those that aren't like OkeyDokey (and feel free to correct that assumption if it's wrong Okey).
I always thought it would do well - 2-5m but not achieve the Wii Fit type sales that people on this site (lovers and haters equally) automatically assumed it would.
Glad you're liking it MaxwellGT2000! Keep spreading the word.