Great job. I've played it once, got to level 7, and was going to stop. But then I saw a comment refer to beating the game, and I had to go back and try again. Still died at 7, but I'll probably come back. If you actually can beat the game, it'd be good to let players know, so they're motivated from the start >:).
I really like how you took a simple rhythm game mechanic and layered a miniature RPG fight over it. While it doesn't *actually* change much (you still want to hit the buttons at the right time), it makes the player feel much more involved. It gives a clear sense of working toward a goal, with a definite end state (many rhythm games just go, without much change or arc, until the song ends). It'd be cool to develop the fight mechanic further.
Again, great job.