There is a good game and systems in there. But I would probably rework the building aspect. Give me more space. I feel like i have to less influence about the fight, i can not really build additional towers that fight, i can only buff things up. and i don`t like that aspect that i cant build towers "on the frontline" etc. Maybe give me soldiers or heros to recruit and put in front of the walls or something like that.
Maybe remove the walls and towers, have me start with only one tower and let me build the wall and other towers myself. Art, Audio, Gameplay loop is fine, besides having to less influence for my taste.
I also used the same asset pack before when i started learning godot, I like it very much. but because everything is so small in your game, the asset pack is not playing at it`s full strength or potential.