This is really awesome!
It reminds me a bit of a top down DOOM with the "shoot all the f**king monsters with ALL the guns!" I also liked the paralax effect you made for the map! (Also can we take a moment to appreciate the music?)
Things I would change are make it easier to switch weapons, number keys did not work for me... And just add more stuff, more enemies like ones that charge to you in straight lines, enemies that shoot back at you and big "boss" zombies that take long to kill, more weapons like a long range sniper and maybe powerups? I could see speed, damage or health powerups fitting in nicely with the rest of the game!