A very unique tower defense game. You use music to defend yourself from the evil notes that assault your music sheet. Now although that might not sound too exciting, it's actually really hard, and I've only played it on NORMAL. :P
The trick is that the abilities of the music towers you place fluxuate depending on the beat of the music. There is real strategy involved with this, so beware you will get frustrated.
There are nine songs in total with at least two difficulty levels. (There could be more, but I haven't gotten far.) If you're a mamber to Newgrounds then you can earn any of the eighteen medals, two of which are secret medals so good luck. For those who aren't a part of Newgrounds, or even if you are, you can download any of the music to the levels you've unlocked.
I say to try it out. It's a nice twist to defense games and if you find some music you like, you can download it no prob.

http://www.newgrounds.com/portal/view/576557