I remember watching The Witch by Robert Eggers and thinking how good it was for his feature debut, as a horror film. Here Ari Aster basically does the same with Hereditary!
You’d be best as well going in not knowing too much, but in short, Toni Collette plays a mother, Annie, dealing with a number of issues after her mum’s (also the matriarch, meaning female family head) death. And as well as Collette, Alex Wolff’s excellent as her son Peter, alongside Gabriel Byrne as the husband Steve, but above all Milly Shapiro does true wonders as their creepy young daughter, Charlie!
The only real thing I’d say then is they could have make it a bit shorter towards the end. Lines between reality and fantasy become more and more confusing and it’s clever, but it does become a little excessive. Still, definitely check Hereditary out.