Having looked forward to watching this, I have to confess to being quite disappointed. A strong build-up, with a nice line in dark humour, make the first 30 minutes or so quite involving, and the film has a nice line in creating a creepy sense of foreboding.
Then things get all "Poltergeist"-esque, and the movie moves from one effects-laden set-piece to the next. Despite featuring some still creepy sequences, the tension seems to run out of the movie before we're even at the last act. And then it can't seem to decide whether it wants to be a ghost story, a psychological thriller or an analysis of grief and mental illness (seriously!)
After such a strong start, I was left disappointed and deflated when it ended.
As a point of reference, horror movies I like include: The Exorcist, The Thing, Poltergeist. The Shining, Texas Chainsaw Massacre, Salem's Lot.