Audiosurf

I've become hooked on Audiosurf. If you download the demo be aware of two things, first you need to get Steam to play it, and second you'll only be able to play five songs.

The US$9.99 is worth it though, especially since the real dollar (Aussie) is nearly at parity.

As I said, I've become hooked.

What I have found is the following:

1. The hardest song that I have encountered is "Million Way of Drum" by Force of Nature. I guess that's how the game engine designates blocks and such because there are millions of them since the song is basically, as the name suggests, drums (there is a bass guitar in it for a little bit as well).
2. The songs "Kalinka" and "Korobelniki" as sung by the Russian Red Army Choir give plenty of red blocks.
3. I haven't tried it yet but I think that it would be entirely possible to listen to say Skeptoid while you play. I don't know if it recognises a difference between podcasts and songs.
4. No matter how obscure you think something is, there will usually be someone who already holds the #1 spot.

I'd say get it and have fun. The game is fun, and the music is always excellent.