I'm just gonna copypaste my thread from FFS~
This was floating around /v/ today and I finally got around to playing it just now.
It is excellent. Basically, what you do is pick a song you want to play and then ride a highway of coloured blocks that appear on the beat of the song. When you complete a song, you send away your score and compete against people around the world for the high-score.
Edit:
The trial is over. It'll be out sometime in February.