I went to my brother's apartment and played this game he just bought. It is soooooo much fun. It goes off the same concept as DDR but you use a guitar as the controller. You play along with songs and you can hear your character mess up when you mess up.
It doesn't take any knowledge of music either. It's just pressing a color button found on the neck of the guitar (and flipping the strum tab) as the color (each color has a deticated location on the screen) comes down on the screen. It's a bunch of fun.
Check out some of the videos and stuff:
http://www.guitarherogame.com/