Audiosurf is nominated in three categories for this year's Independent Game Festival Awards; grand prize, audio, and technology. It's an interesting combination of a music visualizer and a match-three game, with elements of a racer.
When you start a game, you're asked to select a piece of music, with the application defaulting to your "My Music" folder (but navigable anywhere, including to, say, a CD in the drive). Once selected, it builds a race track from your music track; I'm not clear on the algorithm involved, but "intensity" corresponds to slope. The point here is that the same piece of music creates the same track, so that if you select, say, "It's Better at the Matinee," the track you're presented with will be identical to the track generated by someone else who selects the same song on his own machine.
You pilot a sort of hovercraft down the track; there are several different vehicles available, each with slightly different characteristics. The track consists of three "lanes" with shoulders to either side; tracking your craft, below you, are three "stacks", each with several squares arranged vertically. This is, in essence, the "board" to which you "play" colored squares in an effort to creates abutting blocks of colors consisting of 3 or more squares.
Blocks of color are stationary on the track, and as you race, you can slide left and right to intercept them (or avoid them). Thus, if say there's a red block coming at you in the left lane, and you want a red block in your left stack, you slide over to run through it--but if you don't want a red block there (because, say, there's a blue one in your left stack and you're trying to grab more blues there), you can avoid it.
Each time three same-color blocks are properly arranged in your stacks, they disappear, you score points, and blocks atop them slide "down" to the base of your stacks, Tetris-like.
There are some power-up blocks as well, including wild cards (matching any color) and ones that transform everything in your stacks to the same color. Also, different colors score more or fewer points, with "hotter" colors (closer to red) scoring the most.
By registering at the website, you can upload your high score from a track -- so you can, in essence, compete for high score with a particular piece of music against everyone who has "played" that particular track.
One notable aspect is that the game seems more enjoyable with techno or jazz; the backbeat of rock causes bumps in the road with each drum-hit, which I (at least) find somewhat annoying.
It's not the kind of game that I personally am going to play obsessively; I'm not a twitch gamer, and match-3 games are by nature fairly dull. But I can readily see firing it up from time to time to kill a little time more enjoyable that with, say, Free Cell. But the "compete against the same musical track" aspect will, I'm sure, obsess some players (nothing like a leaderboard to make that happen). And on the whole, it's a novel and imaginative approach to the problem of making gameplay dependent on music.