Lots of people have talked about Audiosurf since it hit Steam a few days ago. This is exactly what Steam should be for, a hub for these cool indie games so they can reach the sort of mass audience they deserve (see: Introversion).
I see Audiosurf as a combination of Phase, Frequency, Columns and a virtual rollercoaster. I like all those things so having them together for only a quid or 2 more than Phase on its own is brilliant. If you got Phase but were a little disappointed then try this out, its a lot easier to use and the right sort of complex to play.
As for high scores, its one of those things where its easy to get gold medals but hitting the top 10s will require mastery. Of course, you could just find a song with lower scores.
Its blisteringly fast when a song kicks in too, I like that.
Audiosurf is on Steam now, it costs $9.95 or you can download the demo which lets you play any 4 songs. It also comes with The Orange Box soundtrack and Still Alive makes a brilliant track.