This movie is excellent.
I went into it with absolutely no knowledge about it. Zero. I caught an early matinee and was the only person in the theater. Eward's post describes it best -- it was an absolute fucking freakout.
I'm not surprised to see a lot of comparisons to The Witch here. It shares many similarities with that one -- not just thematic either, but also in the structure and pacing. I saw so many parallels that I think that Egger's movie had to have played a big influence on this.
Dealing with the kind of supernatural subject matter that both the Witch and Hereditary do can be quite precarious for a movie. You're just a hair's breadth away from becoming ridiculous at any moment. Eggers pulled it off flawlessly, IMO, with a directorial virtuosity that continues to astound me. On the other hand, I thought Hereditary stumbled in a couple instances into dangerous territory. Aster, to his credit, does manage to quickly steer it back on track though.
Another minor criticism I have is with the movie's ambiguity. To again compare it with The Witch, that movie, though it invites varying and even contradictory interpretations, was very unambiguous. After you see it, you don't question what, if anything, represented onscreen was real and what wasn't. It was all real. With Hereditary, I'm not sure what the hell really happened. I know a lot of people actually like that quality in a movie, and I do too sometimes, but I'm bothered by it in this case. I guess it's more a statement of personal preference than a criticism.
Minor quibbles aside, I thought this movie was fucking amazing. I don't think I've ever been this fucked up by a movie at a theater. It took me a good 20 minutes or so to come back to down to Earth after I left this one.