I picked up Beat Hazard today, so I've started with Ultra and never played Classic.
At first I was dissapointed, but now that I'm getting a feel for what's going on in the game, I'm starting to like it.
There are only two things that annoy me now:
First, you can barely see where your ship is at times, but I guess that's just getting used to the game
Second, I hate the music browsing. Good thing they added a windows browser, otherwise it would be near impossible to browse. Then again, this is one of the things I don't really like about Audiosurf either.
I'm still more pro-Audiosurf, as it is an easier game for your eyes and mind, and thus much more relaxing, even on the hardest of songs. Beat Hazard is a fun run though, for that times you really need to just blast it all away.
I never understood why a music game would let you start with low volume, though. Good thing there's a perk to fix this.