One of the few films that would have benefited from an ambiguous ending.
I enjoyed the film a lot, especially in the way it toyed with the prospect of Rosemary not being all the right in the head. It keeps you back and forth on believing her and not believing her, which is why I think ending it right after she gives birth and sees that her husband has no mark would have been a perfect ending. I normally think ambiguous endings are a cop-out, but in the case of this film, it would actually fit thematically, as a viewer from Rosemary's perspective could never truly know what the truth was.
As it stands, I think the ending was a little bit too much for me. Showing the true motives of the cult in such immense detail kind of took away the creepiness factor, and kind of breaks the cardinal sin of horror in not leaving as much up to the imagination of the audience as physically possible.