Pretty cool idea to invert the way a tower defense game usually works. But the big issue with this concept is, that it’s to easy. You can just build a wall of turrets which then block the path of the incoming enemies. I think the price for a turret is way to low and for a upgrade is to high. I didn’t even realize you could update the turrets, because it was way more efficient just building a wall of towers, and with that having no problem beating the game.
Also when you do that and you have a lot of turrets the game starts lagging quite a bit. I still think it’s a cool concept, but it needs work with the balancing.