Not much complaints here. Nice little game with hit detection, movement, controls and other basic things working well.
Perhaps the window is too small (although the information fits in well enough). Pause button gets on the way sometimes, and I clicked it accidentally while shooting. "Restart" should probably read "resume" in pause menu.
Very good start for Unity developing. You could try adding some moving enemies, bonus items etc. And perhaps some variance with weapons that don't require constant clicking. My finger hurts.