Meh

You need a penalty for letting the soldiers pass.

okay

its a good start but it needs many improvements.

You need levels, different guns, upgrades, different enemies and headshots.

Also why do the stickmen have guns? They never fire um o:

boring

very quickly becomes boring, only 1 lvl, no health and no ammo, not very good...

a start, but there could be more

A very nice start, but it doesn't get you very far. I would recommend improving it by several factors.

Add some sort of difficulty by a penalty if you let stickmen escape, Also some bonus if you achieve headshots.
Maybe you could add different kind of weapons? Also maybe you could limit the ammunition.
Also there should be some level end and not always the same wothout end.

As I already said, it is a start, but it gets boring extremly quikly.

The glitch of being able to kill several enemys (already mentioned by others) with one shot would be nice with a shotgun, but it is strange with a handgun (or is it actually intentioned?).

to easy

1 add lives to give the game an objective
2 separate headshots and body shots
3make the zombies and or gun reticule smaller
4 add levels