I watched this film without knowing much about it in advance. I'm glad I did, otherwise I might have been influenced by the very negative reviews on this site.
I thought it well written, acted and filmed. Focussing on the ambiguity of the story - is it a film about ghosts and demonic possession or is it a film about female hysteria - made it, I think, very interesting.
I have not read Henry James's original novel so have no opinion about its adherence or not to the novel. Given that all dramatisations of novels are likely to change the original to some extent, I see no problem with that. What really matters is producing a watchable, engaging film. That is exactly what I saw here.