I have a few suggestions in regards to the gameplay:
First off, make an incentive to put down the turrets, as i do not think a number on the top right is enough. I do have some suggestions though (making each stage require a minimum score and you'd die if you don't have enough, or spawning enemies and having the turrets target them while you simply avoid their shots; score can be calculated by the amount of enemies your turrets have killed).
Secondly, make the turrets more random, to make it harder to stay in a "safe-zone" where turrets just can't shoot you.
other than that, this game is amazing, audio wise it's incredible although some BGM would've been better imo, visually it's appealing and the background is not bad although making it change each stage would've been better imo, creativity wise it's a pretty novel although more twists on the idea would've been better imo, approachability wise it's pretty easy to understand the controls, although a difficulty setting and some indication on where you can place your turrets would've been better imo.