Alright in concept, I just want to share a few things that need improved on. I've only played the first level marked as Easy and don't find the game motivating to keep playing. Here's why:
1) The hollow thud-like sound when I press the keys interferes with the sound of the music. It doesn't match any pitch in the song at all, so I feel like I'm banging a kid's toy drum over a much better song and ruining it.
2) The key controls worked just fine, however, the full-ring where you need to press up-left-down-right all at once doesn't register on my keyboard. I'm sure this is a hardware issue because I don't have an anti-ghosting keyboard (I believe is the term). It is still something to consider in design if too many keys are expected to be pressed at one time. Game-pad support is only a limited solution.