A silhouetted figure stares down at the blissfully unaware camp counselors during the prerequisite "let's all gather around the campfire and tell scary stories about the guy who will be ripping us apart in the next ten minutes" scene. And your haunting soundscape ignites our imagination with what grisly horrors await Madman Marz's victims. We get so much with so little! It's too bad the rest of the film fails to live up this early tone of dread and unease.
This is also one of the few times we actually see Marz. His time onscreen is fairly limited, which doesn't give him much of a chance to establish any sort of personality compared to the other genre icons near and dear to our hearts. However, due mainly to your very effective use of sound, we don't need to see him. The heavy, labored breathing you laid over the POV shots, along with the animalistic shrieks and growls that punctuate the gory set pieces, means Marz nonetheless becomes a madman to be feared.
(Drinking game: take a shot every time I write the word "madman"!)
Your sound effects also impressed me in the flashback of a hulking farmer inexplicably slaughtering his family. Given the subject matter - young children being slaughtered - it could have easily dragged the film into the territory of nasty, needless exploitation. But the way the violence is tastefully toned down, mostly implied by the sound effects of the killer's booming footfalls, make this entire sequence incredibly unnerving. Let me tell you, Richard, it rattled in my head long after seeing it.
Other times, the violence gloriously explodes in front of us, like when a character peers underneath the hood of his car, only to have Marz bounce off the hood with a thundering metal drumbeat and decapitates him. It perfectly sets up the next payoff, in which another character wonders why the car won't start and quickly finds out it's because "AHHHHHHHHH there's a severed head stuck in the engine!"
But, here's where Joe Giannone's script and direction let you down.
When Marz isn't a) stalking the counselors, or b) performing lethal spinal enhancements (I'm better off not knowing which foley effect you used for that one), there isn't really a heck of a lot for you to do. I realize we're talking about a teensploitation slasher film, but it still might have been nice to see a narrative more complex and interesting than: character A and his fantastically huge belt buckle going off into woods, disappearing, is searched for by character B, who, after meeting his maker, is searched for by character C…and so on and so forth.
That standard sort of plot structure can work, sometimes. But not when every character is a screaming bore and so completely devoid of personality that you're checking your watch every ten seconds, wondering why they aren't being dispatched by the resident madman (drink!). I don't need profound character drama, but anything that might have made these people more likeable and interesting (a personality, say, or a motivation more complex than the desire to reproduce) would have been greatly appreciated. It's the cardinal rule of horror films: if you can't bring yourself to care about the characters and what may happen to them, there's little suspense to be had. They become nothing more than meat for the grinder.
Oh, and one last thing: I'm not sure if you played part in the toe-tapping bluegrass tune that closes out the film, but it was truly inspired, and I've been humming it for days now. Bloodthirsty maniacs definitely need their own theme songs.