The visuals is really the best element of your game, I always find something unique in this older art style with tape cassettes etc. The melody is nice as well, and compliments the gameplay.
I have some suggestions for you. First of all, I don't like that the character sticks to the wall if I didn't jump high enough, reducing or removing friction can help. Also, I would rather control the gun with my mouse, but probably it's just a personal preference. But overall, the game is really appealing and cool, nice job!