Ending did feel a little off, but I think they were trying to get at deeper symbolic meaning at the expense of losing the most satisfying horror ending. It's basically a story about family relationships and how they deteriorate and how they can be salvaged. Although ultimately the family bonds are only saved here by preserving the dark secrets from their past. Father passes the burden to his eldest son, who becomes the new secret-keeper and head of the family.

I'm not totally sure what the filmmakers were trying to say with all of this, but maybe somebody smart will show up in this thread with a good take. Anyway, I'm still on the fence about the choice for the ending, but I can see why they made it.