Very cool! Good to see another Godot entry. The main issue I had was the audio. The shooting sound can get a bit annoying to listen to after a while. I recommend changing the pitch of the sound randomly whenever it plays. You can do so like this:
(path to audio stream player).pitch_scale = rand_range(0.9,1.1)
(If you use this you probably wanna put it above the line where you tell the audio stream player to play.)