Game is really good, but I think, there could be more. Only 4 towers, that aren't upgradable and the upgrade system could be a littlebit better (maybe a skilltree, where you can spend points you get from a level-up in certain talents). But not bad at all!
I definitely like the graphics in the backgrounds! But all the other "Edmus" (or how the black things are called :) ) are just replays. In one run I had myself in front of me as a previous gameplay.