I have no sense of how many levels I've played, but the player is hampered by unclear directions/explanation of where towers can or can't be placed, and it seems very unbalanced in the player's favor. I can avoid further building for dozens of rounds at a time, then suddenly the skill jumps, I build, and I go back to doing nothing. Give me a goal, a certain number of waves, larger or faster waves or more enemy hp or... something. Good effort, though! Not buggy, just needs some tweaks.
I will fix when I have time :)