Very fun! Though I do wish expert posed more of a challenge. I'm only OK at rhythm games, and expert was a bit of a snooze fest for the majority of the time, until the last 3 opponents, and even then it was only interesting for a small part of the song.
I'm also not sure whether the incremental style made it more fun or not, as it only really served to force me to play the first few songs multiple times. It probably does help newer players not get stuck though.
Overall, very neat idea, and was still fun, but could do with some more challenge.