I was reminded of another horror story that I recommend to people - The Monstrumologist, by Rick Yancey. It's a series, but I've only read the first because the first one is so gruesome and creepy. It takes place in Victorian-era New England and the main character is a young lad who's essentially been apprenticed to a scientist who specializes in monsters. The action begins when someone delivers the corpse of an Anthropophage to them. It's a "real" mythical creature that was believed to exist back in classical times and has since been (apparently mistakenly) described as humanoid but with no head. Its facial features are in its chest. Yancey's take on them goes with this depiction, but they're very large and extremely dangerous. They tend to feast on corpses and have set up a nest in a nearby cemetery, but they're becoming numerous enough to be a danger to the living as well. It's a hellaciously good read but it does have a lot of truly gruesome scenes. It never went so far I wanted to put it down, but it surely went right up to the line and dared me to keep reading. I'm glad I finished it, but I'm going to have to be in the right mood to tackle the first sequel, which deals with the Wendigo. That's one of the things I really liked about the book, that it deals with not just real world legends but some of the more obscure ones, rather than being Yet Another Vampire/Werewolf Story (tm). And also, wonder of wonders, not a single person anywhere in the book is romantically attracted to the homicidal monsters. You have no idea how refreshing I found that.
Another author who goes right up to the edge of my personal "Nuh-uh, no more" line is Richard Laymon. I'm reliably informed that some of his books cross the line, but none of the ones I read are overly gruesome or explicit. They are gruesome and explicit, very much so, but in ways that serve the genuinely creepy plots and are only gratuitous enough to make sure you're paying attention. If that makes any sense, which I know it doesn't. Laymon does have a tendency towards the written equivalent of what's called torture or gore porn in movies, but for me at least it's much easier to take in literary form because he doesn't dwell on it. He gives you a very disturbing visual and then moves on to the next one, and the next. He also tends to explore the darker sides of the human psyche. Even many of his protagonists have really creepy thoughts and actions, though the books I particularly liked had normal, more or less decent people in bad situations rather than deliberately causing said situations. The books I would recommend are
A Night In The Lonesome October - a college student starts wandering his town late at night and encounters some truly, truly strange people. Some good strange, some sad strange, some very bad strange. The people he knows in his daytime life turn out to be not so normal themselves.
One Rainy Night - a black rain starts falling and everyone touched by it is turned into a homicidally insane killer. Boom, instant plot token, let's get straight to the action. Laymon's good at those.
In The Dark - a librarian finds an envelope with a clue and a fifty dollar bill inside a book. She follows the clue and finds another clue, and more money. She keeps going and does more and more extreme things for more and more money, until she realizes it's far past the time she should have stopped, but she doesn't want to stop. And the Master Of Games won't let her, anyway.
Midnight's Lair - A large cavern system has been turned into a tourist attraction. Half of the system has been walled off for a century because it was deemed unsafe. When the power goes out while a tour group is right there at the end wall, though, the guides decide that breaking through the wall and heading out that way will be shorter and safer than trying to make it back through the winding path they've already taken using only portable lights. This seems logical enough, but let's just say it turns out to be a mistake. This isn't Laymon's best, by any means, but I like it because of the truly, truly creepy premise that could conceivably work in the real world. I'll happily PM it to anyone who doesn't want to track down the book but does want to be creeped out.
The Traveling Vampire Show - Three teens in the sixties, two boys and one girl, sneak into a traveling carny show that claims to have a female vampire that is willing to fight anyone dumb enough to volunteer. That's the basic plot, but there's so much else going on in and around the characters, both supernatural and not. It's very much a coming of age story, with the main male character trying very hard to understand his female friend but clearly missing a lot of what makes her tick. I'm going to have to read it again, because I can't even remember most of the details. It's not nearly as thin a book as the simplistic plot description would suggest, and it's the other stuff that makes me recommend it.