This is a really creative idea. The visuals are well polished, and the gameplay is really fun.
I think difficulty ramps up pretty quickly, and you can easily find yourself in a situation where you can keep up and snowball into 0 hp.
I think the fact that you need to click on enemies, but also move your mouse to place blocks and turrets contributes to it. Maybe adding some hotkeys would be a good idea. Also later on it’s easy to lose a turret just after placing it, and end up without any scrap. And I feel that the 2nd turret is weaker than the 1st one.
The rules for block placement can sometimes be frustrating, if you try to place a block in a hurry. There at least needs to be a clearer indication if you can place a block. And tbh the original tetris rules would be a better idea - place blocks wherever, but they fall down.
But overall, this is an amazing entry!