Good start!
I going to either guess English isn't your first language or you just didn't care about the dialogue's grammar. It's a good game, kind of short but entertaining! I played through the first time using the pistol thinking I was going to conserve my ammo for a later period in the game but it was too short for that later period. I found a good way to conserve shotgun ammo was to shoot one round into a zombie with the shotty and then switch to the pistol for the final blow. It doubled the amount of zombies I could kill with it.
Overall it's a good start for a zombie game, hopefully you'll develope a sequel or another plotline for a zombie game. Perhaps look into a game envolving a government follow-up investigation into the cavern? Perhaps a story of the original zombie break out with swords, pikes, and the like. Again, too short.
Improvements: Obviously make it longer, possibly prioritize checkpoints on the mini-map so they pop up as objectives change or they indicate which one to do first.
Add a reload button for the pistol (possibly the other guns as well).
Add more weapons, or ammo boxes, and improve upon the weapons and the aim. The shotgun handled like a rifle with no spray and general accuracy. Maybe make it fire numerous pellets that spread out, each pellet doing a designated damage amount thus when close it does more damage when more pellets hit but far it does less since they're spread out and are more likely to hit more zombies rather than a specific target?
Add a pause button.
These are just some suggestions that I think could improve any future zombie projects or shooters you create. What you did was good though, and it's a lot more than what I can do so you get a thumbs up and a smile from me. Good job!