Once I figured out what was happening and that the minions were on my side it got more fun. I think you have too many upgrades to stick on just two buildings, I would make some more and spread out the upgrade tree a bit. There's no feedback as to how strong your minions are, so you can't see how the changes in your towers really affect their health and weapons or whatever, which makes optimizing your placement kinda guesswork. I think a grid system for tower placement would help a lot too. Once I got all my towers set up and explored all the upgrades, I had no idea how many bosses I had killed so I quit.