Essentially you feed in an audio track in one of several popular formats, AudioSurf then analyzes the music and generates a racetrack. On this racetrack ride several coloured blocks. These blocks can be collected in a grid, in much the same way as Connect 4. Once you have collected three or more of these blocks of the same colour in a connecting pattern you will score points based upon the number of blocks and the colour.
There are variations on the theme giving your character special abilities such as pushing the blocks to the side to create more complex patterns, or “mono” mode in which you only have one colour to collect and one to avoid.
Because the track is generated from music the number of tracks available is only limited to your music collection, equally two people can compete on the same track by feeding in the same music.
If you get a chance and have $10 sitting in your PayPal account, it is available on Steam. My current favourite track is Fire Fall Down by Hillsong United.