I've just finished this version!
I think what you should primarly work on is the ennemy's AI. You can finish this game without taking damage by hiding inside a building.
Also my gun turned into an uzi by pressing the "auto-click" key of my mouse, a delay would be good.
I took some collectibles while my energy or my life were full, I wish I could let them still then take it later when needed, but they despawn... At least you shouldn't auto collect them while you don't need them.
Also I get it that the big fire spiral that came from the zombies is a way to know where they are.. But when they're surrounded by firer like that it's almost impossible to aim.. Maybe add a bit of transparency?
Finally the boss design was nice, but you forget to remove a print when you shot it:
The sound effects were funny, the fire explosion was a bit too loud tho.
Congratulation for this work team!