I really like the idea for this app. I teach music, and am always looking for new ways to engage my students. I think 90% of this app is good, unfortunately the other 10% spoils the app.
The app looks great, and is easy to understand. The challenges are set up in a way that teaches and engages the player. They start out simple, but then the tempo and complexity increase as the challenges progress. The only problem I have with this app, and it's a big one, is that the count down into each challenge is "2-1." When you count into a musical measure, you count up, as in, "1-2-3-4." Counting backwards is incredibly counterintuitive and simply confusing. My students find it frustrating, and I have to admit I do too. If I were to make one change to this app, it would be to count into each challenge as if it were a musical measure to be played. Then the app would become a 5 star, fantastic teaching tool. Right now, it's kind of fun, but not something I'd spend a lot of time using, and I wouldn't invest in the advanced versions.