Realism is nice, but the range kills it
I like the fact that you're taking a different look at Zombie Defense games. The bare-bones approach is very stimulating. I greatly enjoy making the best of a bad lot instead of having Smith and Wesson's research labs giving me access to all of their latest stuff. Reloading manually is also a nice touch, though the click-heavy gameplay tends to limit the amount of time you can spend at this.
HOWEVER, your barricades and engagement range leave me wanting to cry. You can't see enemies till they're close enough to hit with a holdout pistol, much less this farmer's varmint piece, which is probably a .223 accurate to several hundred yards. You've got a ten-yard shooting area, and then you use up 6-7 yards with barricades. The enemies enter the screen and they're already attacking the barbed wire. The mines should be placed inside the iron cage, or the iron cage should be MUCH smaller. In actual defensive layouts, mines are always the last line of defense, because you can't guarantee any given enemy will be close enough to trigger them.
It's good work, but in terms of a shooting game, you very badly NEED MORE RANGE!!!!!! Anyway, it is good work, and I'm rating you 4 on the other scale, because of the attention to detail. Keep working hard.