Hereditary is one of the new breed of horror movies. There aren't a lot of crescendoing music with jump scares, and the movie does not rely on gore, although there is some. What Hereditary represents is a leap forward for the genre. The performances here are stunning, with Toni Collette absolutely stealing the show. There is a particular scene of loss where her reaction is physically painful to watch.
This movie creeps up on you, and doesn't ever treat you like a dumb movie goer who has to have every character's motivation beat you over the head, so it's a terrific example of "show", over "tell". This, along with Mandy, ended up in my top five movies of 2018. Watch it. Then watch it again.