needs lots of work

-Very repetitive
-The zombies look just like the humans
-only one gun
-no upgrades of any kind/ nothing to work towards
-zombies dont interact with humans
-One objective throughout the entire game

brains?

zombies eat brains, they dont go hide in a cave...
I see where you want to go though, gameplay wise, needs more work and thinking things true, but keep up!

Failing

Audio analysis:

~You had a mute button for both the music and the sound effects, so that is definitely a huge plus. However, your music wasn't all that great and could benefit from a track selection. And it can't be argued you can add one, your game is only 474 KB.

~The sound effects you had were basic at best. When the zombies died, they sounded like they said "oh." I didn't really here anything from the civilians when I killed them, so there's something you need to fix as well.

~Gunshots need to be more realistic, the out of ammo click noise is ok but the reloading noise is not.

Gameplay:

~Simplistic in nature and easy to understand, just like the rest of these types of games. It's easy to learn and do with no real control problems.

~The gun reload time was unrealistic, it should be longer with more sound effects.

~It was too easy to spot zombies and civilians. Civilians don't even have health bars.

~You use a pistol to kill zombies in "Zombie Sniper." I feel this is... misleading.

~Zombies pose no threat to civilians.

Content:

~You had a well explained instruction page that covered everything that needed to be.

~You had a pause menu, always a good thing to have.

~There was only one gun in the game. You need to add more.

~There were no powerups or items. For example: pills that would slow down time temporarily or barrels that would explode and cause multiple zombies (and possibly civilians) to die.

~There is only one mode, there should be an infinite day mode and a timed mode. There should also be a variant that requires you to guide a civilian unharmed by zombies from one location to the other.

~There is no quality select.

~There is no save feature.

Plot:

~Here is one of your weakest fields. First, you stop zombies from entering a cave? Seriously? Why is it important they don't reach the cave?

~Since the zombies are no threat to civilians, there is almost no point in killing them unless their disease is contagious. I doubt this because the civilians are obviously not alarmed by their presence. And you can't say it's because they're disguised because it's pretty obvious that they're zombies.

~There are no cut scenes. There are very few games that would benefit without them, and this one is not one of the games that would. Add cut scenes.

~The main character has no goal or reason to do ANYTHING. He doesn't even switch locations or get further or closer to the cave. We as players don't even know why it's bad to kill the civilians other than loss of health.

Closing statements:

It's good for just doing a shooter game, but it has more than some room to improve. Keep trying.

I've seen better

It's way to simple.
As mentioned before you should add upgrades, upgrades to weapons and base (cave). Add Infinite Days.

I think at an attempt to make a shooter this is

great.
I guess the only problem would be is that is faces up so so many sniper/shooter flashes here on NG. I reckon that the music was great, your art was lovely and the difficulties were nicely milestoned, however I think there should be more attempt at changing the appearance of the zombies and civilians, after all it becomes pretty obvious who is and isnt a zombie thanks to the life bar, yet using the same character makes it a bit cheap. Also you could throw in a different type of gun or something, maybe a secondary weapon.

Oh and why are the going into the cave? It's better they're in there rather than our cities! :P
I'll throw you a 4/5 6/10 to level you out.