I got the demo for this on Steam a few days ago, and not long after got the full version (Though it took a little while for it to realize it was a full version not demo annoyingly). It's yet another music sync game, but it's pretty awesome as they go. It reminds me of another game I like called
Torus Trooper.
Basically you use your mouse or keyboard (Or both in two player, one controller per person), to move your rocket ship left and right and score points. There are a couple different modes of play, etc, etc. But the cool thing is this, most of these music games limit you to a small library of music, but Audiosurf works with your own DRM free music (I like to play to Daft Punk), it creates the tracks for them dynamically!
It's really cool, you don't have to buy tracks, there are multiple play styles and colors (It's even a little trippy). Hell it's just fun to watch, I could totally see someone playing this on a big screen at some night club with everyone watching as they danced and listened to the DJ (So long as they played the same song as what the club was playing).