Dude... Audiosurf!
There is a demo out for a reasonably recent game called Audiosurf on Steam at the moment. I bought this game simply because of Jeff Gerstmann's (Giant Bomb) various quotes during podcasts, "Dude, Audiosurf is awesome!" He is totally right.
While the game lacks a direct story mode or anything the reason is because the music library that the game uses, is your music library. Audiosurf is a game that will never suffer from people wishing these songs or those artists were in the game. The idea of the game is fairly simple, and tutorials demonstrate exactly how to play.
Pick your favorite song and Audiosurf will scan the song and set up the track. This doesn't take very long, but the game tells you that the first time you load a song it could take a while. Then you see a layout of the song. When going uphill it is a softer type of music, and downhill runs happen during faster or heavier music.
You control a ship that flies across the lanes on the track, colored blocks flying at you constantly. You either dodge or run into them and try to create combos by collecting blocks that you need. It is hard to explain at this point, but the demo has built in videos that work fantastically for training purposes.
Online leaderboards track everyone's progress on any song you play, which is pretty fun to see. And remember, as your library grows, so does the Audiosurf library. This means to me an infinite replay value. Not only that but there are many different ships with different skills and difficulty levels to keep you playing non-stop.
Audiosurf gets a 5 out of 5, and its ten dollar price tag is way to easy to pay out for something this fun. Download the demo here and play your four favorite songs. I can almost promise you will want to play more and more.
PS: For a really fun song pick one with a bit of dead space every so often. A little pause in the music translates fantastically to Audiosurf. A fun one to see how the game works is "March of the Pigs" by Nine Inch Nails. I pick this one because of its slow and fast parts, and I picked it because it is Rock Band DLC so maybe more people who read this will have played it.