For a basic version, this was really satisfying! I like how you can feel the power increase with each upgrade. However, I quickly became overpowered and was able to basically remain stationary and not get hit anymore! It felt great and I kind of wanted to just grind out a higher score... but the sound got a bit repetitive and I was already too overpowered. If there was a bit of variation in the sound effect of shooting, I might have stuck around longer. I was attacking so fast!! Pew pew pew! Nice start to a survivor game, and lots of room for more expansion! I think it would be cool to see more cell types and definitely some music too! Nice work!
Also just wanted to share this cool Godot AudioStreamRandomizer feature which is always nice for frequent sound effects so it's not so repetitive.