Pretty good
Pretty good game, but I have some suggestions (even though you won't notice because there's 100s of reviews):
Make it so you can only get one score boost from each "note". If you tap the buttons quckly or just hold them you can get 4 or 5 score boost just from one note.
Make a score penalty for missing notes and for pressing buttons when there are no notes for the button pressed.
Sort those out and it will be much harder to cheat.
Also (and this one could be more than you want to bother doing): try to make some cool backgrounds for the songs.
Oh, and try and have a few more songs. I didn't really like those songs, but that's probably just mu bad taste. Maybe have a couple of songs from each main genre? Although I realise that would make the file to big........maybe you could load them from an external server? that way the file on ng would only be a few kb!
Anyway, why am I criticising this so much, it was great, please make more!
Oh, and one more thing (lol): if you made the notes move slower or increased rge framerate or something, it would be easier to see the notes.