Exorcist at least has that "1970s nihilism" context, which Hereditary doesn't. As for Hereditary's explanation, the Paimon thing and what the Ann Dowd character actually does were explained very haphazardly and WTFedly, the Maltese Falcon could have just as easily been messing with that family for all I cared afterwards. Oh well--did you notice that that smiling figure you could barely see in the shadows was also at the funeral at the beginning of the movie? HUH? DID YOU? THAT TOTALLY CHANGES EVERYTHING BRRAAAHHHH!!!
I basically like the movie anyway due to the style, but screw the explanation. Hey, screw It Follows' explanation too, and I liked that one even better!
I should also add that the critics that noted that Hereditary contains one of the most painfully disgusting images ever caught on film are right. I mean, I kind of had to think about it, but God what a gross cruel image. You know the one. Bleaahhhh. I thought of that gross "Welcome To The Machine" video, the way it lingered on a similar image in that video.
I read the book of OFOTCN but really I only remember the Indian guy narrating it--I can't remember what the other differences are with the movie. I guess R. P. McMurphy is a bit different in a 1962 rebellion context than a 1975 rebellion context. And hell, do I even really feel sorry for McMurphy? He tried to murder the nurse, what did he think would happen. Sorry, but the crowd pleasing aspects of this movie just don't get to me much at all.