Ultimately, this film swings hard for the fences and misses by a mile. It didn't even hit, it struck out at the plate.
The film forgets the cardinal rule of storytelling: Don't get so lost in trying to send a message that you forget to write a story. The theme, while liberally lathered, suffers for want of reach and palatability, and thereby completely alienates the audience that could benefit most from a good dose of reality: those who perpetuate a toxic cycle.
The plot is almost entirely non-existent, and what little does exist falls flat in an anticlimactic third act that ends without resolving any of the points that were opened along the way. The narrative was by far the weakest aspect of the film.
The characters are somewhat flat as well, though I felt Buckley and Kinnear did a fantastic job portraying them as best they could. Sadly, Buckley's character Harper remains static for the entire film, because, again, the third act fails to demonstrate how her emotional journey has concluded, or changed, or mattered for that fact, and leaves the viewer feeling disconnected.
The classification of 'horror' only applies to the film loosely, and, if anything, falls under the psychological subgenre. No jump scares, no chases, no stereotypical action, so if that's what you're expecting you will be sorely disappointed. Well, you'll likely be disappointed regardless of your expectations, but particularly if you're looking forward to "the first horror film of the summer".
The best part of the film was the lighting. The only moments of true suspense were entirely light based, and they did a decent job of it, though the tool is a well-known one at this point.
In summary, if there's literally any other film in theaters you haven't seen yet, see that instead. If not... don't waste the money unless you have a pass. Wait for the bargain bin.