Interesting game. Graphics and SFX were good. Seems pretty clear what everything is.
The different tower defense structures within the game is an interesting twist, that I enjoyed. Didn't think expanding was going to be as hard. But now that I've got the hang of it I think I would approach the econ of this game differently as a player. I'll echo others that a speed up could help with the flow of the game. I just kinda let it hang out. As a tower defense should be.
Great submission!