sorry for bad quality

The player's bullets need to be MUCH bigger, and overall the key game elements could do with being brighter. I'd make the background colour a dark grey, and enable bloom. There's a post here about doing it in godot :) https://godotengine.org/qa/3776/how-to-make-a-glow-effect

The enemy's bullets want to be brighter, too, and the "flash" effect when things get hit should be white - not a red overlay. There's a post about doing that here: https://www.reddit.com/r/godot/comments/7irdne/how_to_make_a_sprite_flashing_whi...

Otherwise, though, it looks good! I'd make the enemy briefly stop firing every few seconds, just to give the player a chance, but otherwise it's looking good!

I can't give as good a feedback as Chief did but I can tell from my experience that adding sound effects and music makes a game alive