It is a masterpiece. It enters with brutality in the non solved pains of our family archetypes, with a heavy dose of spiritual horror development, a disturbing use of music and actors with anthropomorphic features that increased intensely the artistic intent.
The horror is just a cover up to show the pain of the soul in family issues when the death of a loved one gets into the mix (which is one of the worst experiences a human can have). Hard movie, it cannot be analyzed with the classical horror lens.