Audiosurf turns your music collection into levels in a racing puzzle game.
Point it at almost any music file and it'll quickly generate a unique racetrack based on it. Don't look for identical beat-matching, though - instead, the tracks undulate with the speed of the song and grow more frenetic and colourful during the most intense sections of the music. Audiosurf's greatest achievement is that it seems to reflect the way music makes a passionate listener feel as much as it does the structure of a song.
Its weakest element is the block-collection game that takes place on the music-generated track. Your goal is to stack related colours and avoid others to win points. Audiosurf then uploads your tally to a global scoreboard - so if anyone else has used that song, you'll see how your score compares. This is great when you're warring over a specific track with a friend or two, each desperate to snatch the number one spot.
Audiosurf is best seen as a new way to enjoy your music than simply a puzzle game. Several modes are on offer, which involve collecting a single colour, for example, or having the ability to push errant blocks across the screen. After a little experimentation you'll find the one that suits you best and hits the right balance between a response to the music and a challenging game.
As a game for people who love block puzzles, Audiosurf isn't hugely impressive, but for those who love music and crave a new way to interact with it, it's is an absolute must.