The game is simple and fun. Loved your pixel art too. I would say, the music needed to be changed to something less pitchy. The enemies started to attack without even being visible on the screen. So, I just kept firing and guessing where they were. What I did to handle that was to attach a trigger box to enemies and allowed them to fire only when the player entered the trigger box. Rest it was a good entry. Kudos to you!
Please take some time to play and rate my game as well, I would really appreciate it! Thanks a lot!!