When you're branding yourself as extreme horror, the worst thing you can be isn't offensive, but boring. That's kinda the case here. There's a workmanlike competence, but the author so closely follows the eighties slasher ethos (or whatever you want to call it) that there's nothing much to make this work stand out. It could easily be, you know, Prom Night or some other schlocky schlock that manages to score Charles Napier and not much else.
It's not that there's one big great gashing flaw here, but the death of a thousand (or five or six) cuts. Let's see if I can make a list.
1. Too much of a slowburn. We spend a lot of time with the various characters and their foibles and I know eighties slashers did this, but that's because they couldn't afford to have stuff happening all the time. Twenty Minutes With Jerks is a TV Trope because it's cheap to shoot actors pranking each other and bantering. In a book with an unlimited 'budget,' there's no reason to spend this much time on stuff this boring. Especially when, at several points, the actual action happens off-screen and is described after the fact. Buddy, write about that, not what everyone's having for lunch!
2. Too many psychos. I know all horror movies are entitled to a douche character that you want to see die, but this book really overdoes it. Not only are there multiple dicks, but they're all would-be murderers! It's ridiculous! Like the author was trying to do a Scream-style mystery with multiple suspects who could be the killer, but then decided to reveal from the get-go that the killer is just a crazy backwoods slasher and made everyone else slasher-adjacent anyway. So we just have four separate rapey psycho killers all in the same zip code for no reason. Come onnnnn... And it's not like anything really comes out of there being multiple murderers. They get diced the same as anyone without their murderousness affecting the narrative. So it just feels like a waste of time and a loss of verisimilitude for no reason.
3. That brings me to the actual killer. He's just an insane hillbilly person. He has some helpers and together, they're pretty much the cannibals from Jack Ketchum's Off Season (or, you know, a million other "evil redneck" stories). That's fine, it's not like anyone has a patent on the evil redneck, but if you're going to make a burger, make a BURGER, you know? Give him something to set him apart. Come up with a surprising, shocking origin for him or give him some engaging bit of characterization. Because author Padavona really gives us nothing like that. We don't even get some haunting description of how he looks. He has welts, I guess. That's it. He's essentially Jason Voorhees with sidekicks and although some characters speculate on where he came from, there's no explanation of why he exists or how it is he can tank being shot, hit by cars, beaten to a pulp, dropped off a cliff etc. Other than "he's in a slasher movie!" I get that nothing is scarier than the unknown, but sometimes nothing is lazier than the unknown.
4. There's not much extreme about this extreme horror. It's not like I want some Edward Lee thing where the writer is trying to gross you out with what sex act is happening to what inappropriate bit of anatomy--that's not horrifying, that's just nasty--but there really isn't much here that would be out of line for a slick 90s teen slasher. People get their throats slit. Ooooh! Someone got hacked up by a machete. Ahhhh! C'mon, you could get away with that in I Know What You Did Last Summer. When you're telling me there's going to be this gonzo slasher movie in book form with no studio exec or MPAA breathing down your neck to avoid an NC-17, I'm expecting people having their intestines dragged out. People being fed their own livers. The good Fede Álvarez, Evil Dead shit. What can I say, a lot of the time it's Supernatural on the CW, blood being splashed on a wall from off-camera stuff. Extreme horror for adults? There's no sex, no rape, and only a few decent kills. Your big play is cannibalism? You think I've never read about cannibalism before? I watched Hannibal! Mads Mikkelsen was baking people into galettes on network television! You need to up your game heah!