I agree with Xavia2nd on all accounts however, I think there are too many plots for the character to move through before it makes one full round. I also think that the player should not need to make that decision when it comes to upgrading the towers. It is such an interesting concept though, and as someone who loves Tower Defense games, it is refreshing and original.
However, I think that the pace of the game should be quickened; enemies should drop more money and the delays between waves should be reduced. Waves should be allowed to overlap to make for a more difficult experience over time.
The aesthetics are also great, and I'm amazed at the shadows of the enemies. This is an amazing game overall.
Question though: how did you make the shadows of the enemies?