$10 on Steam, on sale for the first week for $7.50.
http://store.steampowered.com/app/49600/Another one of those "audiovisual experience" type games. It's a top down shoot 'em up in the same vein as geometry wars, only all the stages play differently (mainly in how your weapons fire) based on what song you play.
http://www.youtube.com/watch?v=IoePn7iMQg4I can't tell if this guy is just really good, or if this is an easy song, because I played on nothing but hardcore for like three hours after I bought it yesterday, and I only cleared like two songs, and only one of those was a perfect. I tried some Infected Mushroom, but they have such a tendency for buildups that explode into absolutely nothing that I'd be left with two huge scary bosses to fight and the music takes a dip and I have no guns!
A lot of fun, hard as hell. Haven't tried easy or normal yet. Don't know if I'll bother.