Supernatural[]
Besides a fallible narrator, one of the central questions in the book is the extent to which the protagonist (the governess) can believe her own experience. Her experience with her surroundings and other characters in the novel suggests that she can not trust her own perceptions of events, that there is something more sinister at work. In that respect it is similar to "Lost", where the characters must doubt and question everything they see and encounter.
Brothers[]
William, the psychologist/philosopher and Henry were brothers weren't they? Their dad was a Swedenborgian. It would be interesting to explore the links between Swedenborg's mysticism and what is happening on the island. http://en.wikipedia.org/wiki/Swedenborgian