I gather this isn't intended for PC, but rather for mobile, given the controller overlay. I initially had some difficulty figuring out the controls on the PC for firing. But after that I've spent a good amount of time on it, it's that kind of immediate feedback/reward mechanics that gets you hooked up. I think one polished more and with more upgrades/etc. It would be a very good mobile game to kill time. (and zombies) :) Good on you trying out Godot, it's a fantastic engine!