Audiosurf might be the first game I bought on Steam...I've owned it for so long that I can't really remember.
What I do know is that, despite the fact that I have owned the game for years, I still come back to it over and over again. Everytime I pick up a new song I like, I know that sooner or later I am going to load it up in Audiosurf and play it. It's easy to use song browser, the fact that you don't have to scan your entire music library like many other "play your music" games, and the classic fun of a match-3 system has kept Audiosurf my go-to music game for 5+ years.
Buy it. Trust me.