There's a simple thing about music games based on legendary musicians: it doesn't matter how much the game helps the player, he'll never be like the original. Hence, it's much better to buy a CD collection instead, and listen to the real stuff.
More commercial and not so legendary musicians, with lots of easily satisfied fans, can most probably sell music games much better. Next time they'll release, say, "Michael Bublé vs. Robbie Williams feat. Avril Lavigne with Celine Dion and Puff Diddy cameos Rock Band" and it will sell like hot cakes.







