Didn't seem interesting at first, and it looked a bit amateurish, , but the actress playing Jessica was compelling and I was intrigued. The use of sound and images to create an unsettling atmosphere was basic but really well done. The sounds were awesome. It didn't take long for the story to pick up. I've watched a few horror movies based on mental illness and hallucinations etc, but they always seem a little methodical. This one seemed more unpredictable, mysterious and natural. I also sympathised with Jessica, and it seemed she had a genuine struggle. There aren't many characters, but they work so well together and create an interesting dynamic. Having so little characters also created more tension, as I felt like I was stuck with these people. There is a bit of a story reveal midway which was a bit clunky, and I wasn't sure whether I'd like the second half as much, but it got good again near the end.
Very odd experience. I questioned what I was watching various times, which I suppose is the point. If I watched this as a child, it would have terrified me. This movie is pretty well made and very unique. Great atmosphere and scary. Despite its flaws it puts many modern psycological horrors to shame.