Good concept, but unfortunately...
The first level (the only one I played) drags on for about one minute after the actual song stops. This is a huge loss to your overall score because, after all, it is a rhythm game. You need to do a better job of coordinating notes with music than that if you want to get good scores.
The graphics could also be more engaging. A black background is boring, and doesn't make the game stand out visually.
Other thing is that you need to make a separate Help screen instead of making a scrolling marquee of instructions. People will naturally click Play the moment the game loads, and since it loads fast, they won't realize the existence of the instructions in time. It's good to have instructions there and all, but since there are no other ways to access the instructions after clicking Play, so players have to reload the game to read them. And fast readers will get tired waiting to read all the instructions at the pace of the marquee. BOTTOM LINE: MAKE A HELP PAGE ACCESSIBLE FROM THE MENU.
But the game is an interesting concept, and it's entertaining to try and focus on playing two games at once. You did it well enough that it doesn't become a balancing nightmare.
So between the good and the bad, it's a 2 from me. Fix up some of the problems, and it'll be 4 material.