So get it out of the "horror movie" genre. Once you view it as a character study, a dark one at that, it may be better reviewed.
With a low budget, the director / producer / writer managed to put together a very well done, character-driven, engaging little movie. The cinematography was very good, the tension was palpable, the dementia was well portrayed.
Thoughts of "Requiem for a Dream" and even "Taxi Driver" went through my head as I watched. Definitely recommend for what it is.