An OK game, but misses the main point:
What makes beatmania and guitar hero is that you actually affect the music. In this game, I can sit there and wait and I can still hear the song, even though I can fail at the song.
But take Beatmania, let's say... every time you hit a button, it makes the currently engaged sound, and as such, it actually matters that you press the buttons on time with the song. Same with GH.
So yes, Flash *is* a bit more limited a programming language, but it's still that little thing that tends to bug me about these beatmania-like games. It kinda removes the entire point out of the game, I find.
A good attempt regardless, however.