People are describing Hereditary as one of the most terrifying movies of all time. I’d say they’re three-quarters correct, in that the first three quarters of the movie were indeed pretty damned unnerving. But then it all fell apart in the last half hour.
For the first hour of so of the movie, most of the tension is derived from having long bouts of nothing in particular going on, punctuated by a tragic and gruesome death. There are hints about spiritualism and a few very slightly creepy elements, but most of the tension comes from the family drama, which is played straight and is both involving and harrowing, and from knowing that bad things are coming (you bought a ticket for a horror movie, after all), but not knowing when or how they will arrive.
Now, this is a horror movie and it works on standard horror logic, which is that the little bad things are just signs or intimations of the Big Bad Thing that will be revealed at the end. For a while, it seems like the Big Bad Thing will be a ghost or a demon. That’s a legitimately creepy possibility, but about halfway through the movie it’s revealed that ghosts at least are already in play. I was too invested at that point to consciously realize it, but in hindsight it’s pretty obvious than anything that’s confirmed halfway through the movie can’t be the Big Bad Thing.
(Unless the point is to fight the Big Bad Thing, at which point, eh, it’s a supernatural combat movie, not a horror movie. Fighting back implies hope, which is the opposite of horror.)
Then there’s the reveal that one of the characters is prone to sleepwalking and sometimes does some potentially awful and dangerous stuff while sleepwalking. I have been around someone who sometimes sleepwalked and would do completely inexplicable things while sleepwalking, and that is also really, truly unnerving. It’s creepy because it sends two questions crawling around the back of your mind: “What might I have done in my sleep without knowing it?”and “What might the people I live with get up to when I’m asleep and they’re supposed to be asleep – but aren’t?”
But then at the end a bunch of previously minor threads come together and it turns out that there is a cult of spiritualists who have been working for some time, Bene-Gesserit-style, to bring forth a demon and assist it in possessing the body of the one of the (few surviving) main characters. Maybe some people found this terrifying, but for me it was a big letdown. For one thing, a lot of the stuff from the very interesting and unnerving first half of the movie simply has no payoff. The family drama basically evaporates as characters are alternatively killed or possessed. Throughout the first half of the movie, a repetitive foreground element is that the mom makes creepy little dioramas as a professional artist, and her daughter makes creepy little found-object dolls (either for fun, or as an aspiring artist – it’s not made clear). There’s loads of potential there, but it doesn’t really come to much, other than one of the daughter’s creations kinda-sorta prefiguring a human tragedy.
So most of the stuff that got me intrigued and engaged in the first half of the movie doesn’t end up driving the plot at the end, and instead we’ve got a coven summoning a demon. And that’s the other reason I felt detached from the ending. A group of feckless, greedy people causing problems by summoning something beyond their control isn’t a horror movie, it’s a non-boring session of D&D. Or maybe just an adventure hook for Trail of Cthulhu. It might be better to say that you could, with thoughtful camera work, sound, and editing, elevate that premise into a horror movie. Unfortunately the makers of Hereditary felt the premise, revealed almost documentary-style, was scary enough on its own. It’s not.
I was also pulled out of the movie when it turned out that grandma’s corpse had been rotting in the attic the whole time, and no-one had noticed. Did no-one on the writing/directing/producing team ever have a mouse die in their house, or hear of it happening to someone else? A thumb-sized rotting rodent can stink up a even a big two-story house for days.
If I’d somehow been called away 90 minutes into Hereditary, I’d probably be lauding it as one of the scariest things I’ve ever seen. It has a lot of brilliant bits that are effective because they suggest – but do not specify – potentially awesome realities, but unfortunately it also has a leaden third act that undoes the previous good by explaining just about everything, just not very satisfactorily. It’s like the Original Trilogy and the Prequels in one movie.
TL;DR: Unexplained noises are creepy. Bodies levitating aren’t. And it’s never good to give the audience half an hour to think, “My level 5 sorceror would have done a much better job of this.”