I saw this game and thought it looked dull or it could be too complicated. Let me tell you. It’s is very simple. The tutorial gives you the tools, lets you play around with them, and then lets you have at it! It’s very satisfying when you figure out a good layout of your towers and just watch them go ham.
I think the only real thing I would suggest is when you upgrade a tower, if there could be a way the player can see what upgraded stats your tower will get. With up to five different towers, I’d like to plan out which towers to upgrade and when. It would be easier if you knew how stronger, or what kind of range your towers will have.
Other than that, it’s honestly extremely close to a perfect tower defense app. Wonderful job.