This game is Audiosurf.
Here's the deal for this "puzzle racer": The game finds a song file, analyzes it, and from there makes a level for the actual game. When you play the game you are trying to collect all the colored blocks. The block then takes up a space on a grid right under your ship. You can see how it works in the picture I've posted. When three or more blocks are grouped on the grid, you score major points! Depending on the song it can be either relaxing and easy or brutally hard.
The best thing about this game is that it's ridiculously easy to pick up but yet hard to master. It's about finding the rhythm as well as good reflexes. There are a good amount of variations, but there's no shame in keeping it simple. I usually just play Mono, the easiest one, because the game is so fun even when I'm not sure of what song I've picked from The Boyfriend's hard drive.
Audiosurf has been out for a while, so I may not be surprising anyone. But if you don't have just go here and buy it. It is worth all ten bucks. That's right, ten bucks for a PC game that uses your own personal soundtrack. That's a great deal.
I know I sound like a sales person, but this game is fantastic and I think everyone should own it.
Only downfall, well at least for me, is that it doesn't have a Mac version. Oh well.