Thanks!
I played up to level 5 or so, and I'm not sure that there's much there that I can give meaningful thoughts on from a player perspective, but I did spot a couple of things that appear to be bugs.
Pressing the right mouse button quickly enough could result in missiles colliding with each other and sliding off to the left.
The there also seem to be timeout signals for each turret that are connected to a function that doesn't exist (_on_Timer_timeout). Was that timeout meant to force a minimum delay between missile launches?
I hope you're having positive experiences using Godot, and thanks for doing a Linux build! :)