Great game! I like the graphics and the UI feels well laid out to me, plus the faces the Ballys have are funny :P It's pretty entertaining until you finish whats available, perhaps while working on new enemies and turrets and such, some kind of quest system could work to provide stuff to do once the player has completed most of the current game? e.g. "kill 40 bally for X amount of RP". I'm not sure how easy that'd be to implement so its just a suggestion!
I also enjoyed the variety of upgrades, and though limited, the enemies and turrets/buildings provide enough variety for now to be interesting too! Though mentions of the shields in the spike description confused me until I unlocked the shield upgrade lol :P
All in all, I had fun and I'm excited to see more! :D
(Editing to add: The copy & paste save is a good idea, but with so many characters whenever I try to paste it in, it lags and I have to reload c': Might just be my computer, but would it be possible to reduce the characters needed anyway?? If not then it's not too big of an issue since the game seems to be loading my save automatically thankfully :P)