The fact that Esther is the "villain" of the picture isn't really a spoiler, since anyone who's seen half a dozen modern American horror movies should be able to guess going just by the premise, or even poster which depicts a suspect little girl with ponytails. No, the devil (so to speak) is in how the events within the film play out, which a lot of the time is structured as Esther causing various problems for her newly adoptive parents.
With the very precise application of often spine chilling atmosphere, and the surprisingly great performances from Farmiga, Peter Sarsgaard and Isabelle Fuhrman (playing Esther), it's all the more disappointing to get to the film's climax to find one of the most ridiculous explanations to what's been going on for the past 90-plus minutes that I've seen in quite some time. Not to give too much away, but let's just say everything slots so conveniently into place with this one laughable and ludicrous explanation that it drags the film way down. In one swift move, the film went from a very, very good example of how this type of horror should be done, to simply an enjoyable chiller.
So even if the ending of the film weighs it down significantly, I still recommend Orphan to anyone who enjoys well done thrills and chills. It may employ one of the horror genre's most overused devices (the creepy little child), but it at least tries to do something unique and original with it. This is The Ring without the supernatural element, or The Omen without the religion.
The film is about 25 minutes too long, with the occasional lull in the narrative that could have been removed to remedy that. But overall Orphan can rest assured it's a more impressive example of mainstream horror than most that gets released nowadays.