Pretty good, but with flaws
It's a pretty good game, really. I kind of suck at it but I'm able to make it to the end (and always end up an unsigned act, lol).
IIt ran smoothly for me, and the graphics were really rather nice, but I agree with the reviews that said the gameplay can get a little bit confusing at times. It is somewhat difficult to tell when the notes are supposed to be hit, and I can't count the times I thought I was hitting them right and they just swept off the screen as though I was too late.
I've played the game through 4 times now, to make sure the issue wasn't just me having bad timing. I believe a clearer indication of exactly where the note needs to be when you hit the button would be immensely helpful.
But, as I said before, it's a good game and I did enjoy playing it in spite of the difficulties and the fact that I do rather poorly. :)