This review may contain spoilers. I can handle the truth.
I loved the atmospheric aspect of it, it's a terrific location piece as well (shot in Quebec!) and I thought Riley Keough was great.
Overall I liked it, but some of it is undeniably clumsy, from the obvious The Thing call-back, the suspicious Hereditary similarities, all the way to the vague and unexplainably dark non-ending.
I get it's like a cautionary tale about messing around with the deranged daughter of a deceased homicidal cult leader, but I can't shake the impression that the final twist, if necessary, felt completely undefendable.