It's a chilling story, with gothic elements similar to ”The woman in black” and references to ”Jane Eyre”, but it's not as thrilling as it's reputation. Perhaps the reason is Henry James writing style, of course rich, but tricky and with endless punctuations marks that usually is rather favourable, but in this case might be considered used beyond all reason.
The interesting aspect is the many interpretations that can be made regarding the ghosts, the children and sanity of the governess. The two children, Miles and Flora, are utterly perfect, both their countenance and their behavior. Perhaps that is why something feels strange about them. The reader might wonder if they are real. What has been speculated and reflected upon is whether the governess is right in her conviction about the ghosts and the children's awarness about them, or, perhaps, that she is psychologically disturbed, imagining things and belonging in a alysum. The author gives no answer, and the reader is left to interpret the story.