Once I figured out how to pick up walls and place them, it became actually kinda fun! It is very barebones, but if expanded upon, it could be very nice.
It would be nice to have the option to skip the waiting period. There were times where I had nothing to do and 75s were remaining. ALSO - the WASD movement shouldn't be dependant on the player's current rotation. W should always be UP, A LEFT, and so on. The way it is now is kinda confusing.
Also, it would be nice if the enemies had clear spawn points. I once set up my defences, only to realise they spawn randomly all around me (if I'm close to their core).
Pretty fun and a nice rendition of the theme!