[full disclosure] I developed this. We collaborated with London Sinfonietta Orchestra to get the pedagogy right.
We aimed to make a game that is both engaging and addictive, whilst also teaching real musical skill (in contrast to say Guitar Hero :o). The pedagogy and game mechanics did clash into each other during development, we did a lot of user testing to find a balance. Raph Koster's Theory of Fun for Game Design was invaluable, as were lectures and posts by Daniel Cook.
It's a hard game, especially for people with no musical background, but nonetheless we had strong engagement.
Players who topped the leaderboard after a few months were invited to perform at a live event. They were pretty good, but then I didn't see them perform before they played the game.