Neat idea! Been long since I played some music-maker type game in Flash. I like how the interface is different for each genre, to match the genre, but for the Rock one in particular the beats just don't feel heavy enough. I don't know the term for it, but there's usually one drum with a snappier sound to it, they're all a bit soft here, and the kick doesn't have that much bass. Also, would be neat if you could click surfaces as well as use the keyboard shortcuts. For the keyboard shortcuts, maybe you could let the user toggle between different types of keyboard to have a layout that suits them best, where the keys are all next to each other? Keep it going!
-cd-