What this show makes me think of, oddly, is Whatever Happened to Baby Jane. Or rather, it makes me think of my issue with Whatever Happened to Baby Jane: I was much more interested in the characters' past than their present. I wanted lots of flashbacks, and lots of secrets, rather than a focus on the present day drama with only one revelation about the past. The Haunting of Hill House provides that for me, flashback after flashback and plenty of secrets. I believe there was one episode that took place entirely in the past.
I think Theodore was my favorite, but I relate most to Nell.
I was not entirely happy with the upbeat ending. Which is to see - I cried, and I wanted the characters to be happy, but it felt too easy. I wanted to the story to be more true to the experience of losing a loved one to suicide, but our characters get closure that people in real life do not.
Also, the revelation of Shirley's affair came too late.