Really amazing game, very polished and easy to play! I can definitely see myself playing this for hours if you added more levels/endless mode.
A couple of minor improvements I noticed. For example, the enemies didn't seem super threatening, I didn't take any damage until the final wave when the big boss almost destroyed me. Luckily using the boost to get a second dragon really helped. Also when you have an odd number of available squares you are unable to use some of your buildings in the bottom right corner. This caught me out and I had to rebuild. None of this detracts from the incredible game however, great job!