I'll reiterate what others have said. This is NOT a scary movie. But it's definitely mysterious and suspenseful. A wonderfully thought out plot line. I went into it without reading any reviews; I only watched the trailer. A little way in, I thought it was going one direction, but I was so wrong.
I disagree with the review that didn’t like the absence of Tom in the end. Just because it doesn't show him, that doesn't mean he hasn't been/won't be born.
I even ignored a call from my parents towards the end. I had to see it through! Very strongly recommend.