Pretty nice-
Too easy though, like everyone else mentioned, with a good sense of geometry you can easily get 100% on all. The levels were very creative, but put the towers at the right corners and done. Unfortunately, without the inclusion of different types of towers and such, there really is no way to improve that dynamic. +DracoErrarus had a good point, there should be levels where you have to pick and choose diff areas to get to a certain %, instead of knowing you can reach 100% all the time.
Also, the art, even though I liked the way you used paper-like things, I think a tv static theme would have suited the game better.
This game must involve a lot of math; nice job on it anyway! Kudos-