Just got my copy from RedOctane, man this game kicks ass, the boss battle with Tom Morello was a ton of fun, he kicked my ass though. Its not a song battle more like riffs, its pretty neat, you get powerups and you get to use them against him whenever you feel its best to use them.
I downloaded a bonus song by Rise Against since it was the only one I knew and was interested at the time...that song is sooo much fun to play specially because it starts slow then gets crazy, then slow again, then crazy again...etc.
Game's a blast!