Got to say Emma Stone delivers her best performance to date imo, I'd like to see her do more out there artier projects and play more bitchy villainous characters. She's impressed me more as her career goes on.
Anyway, Abigail is the real villain of this film. I love that you think that Sarah is the nastier one for a good part of the film, and that Abigail is the sweet innocent one. But that switches around, as much as Sarah is using Anne for power, you can tell behind the "Ice Queen" persona that Sarah actually cares of Anne and doesn't want to hurt her even though she's in her own way a Opportunist. Abigail is just outright a user and opportunist, she sees Anne as her cash cow and stepping stone back into the high life she lost cause of her father. She clearly doesn't give a damn about her husband and only marries him cause of his name and rank.
Although I did love the ending, what I took from it was even though Abigail thought she got rid of Sarah and that she won, but in fact Abigail for all that she gained she blows it. In fact with Anne seen her try to kill one of her rabbits, I think that's the moment Abigail was finished cause Anne knew Abigail lied to her, something Sarah never did (she said she hated the rabbits) and Abigail was back to been the maid she was once she joined. A great ending. That's what I took anyway from the ending.