It's a sort-of sci-fi relationship drama that is single-minded in its approach to sexual dynamics with a handful of characters dedicated to instant gratification. I really liked this film. The story, acting, cinematography and setting were all compelling to me, but I can't say it's amazing.
It presents itself as a mystery, drip-feeding information to the viewer. But it really isn't a mystery. There is no 'whodunnit' element. It is always very clear who does what and why, so the audience is left with very little to ponder or think about as the story unfolds. There are plenty of intentional plot holes (the sci-fi elements are almost entirely unexplored) but they are ultimately irrelevant to the main story. That's the problem. There is no grand metaphor here. There are no conundrums to puzzle over and, after watching it, the questions you have won't be about the characters or the events or themes or what it all means. You know exactly what it all means. You may have simple questions, like who were the couple in the woods? Why didn't they do x,y or z? But your mind won't be whirring with heady concepts, which is what I demand from good sci-fi.
It's a simple film that could really benefit from a deeper subtext or some novelistic elements to give the story more 'meat'. However, as a streamlined drama that takes a prurient look at sexual frustration and secret desires, it's incredibly well presented and has mostly excellent performances. Overall, it's a bold and very unique story. Movies like this don't come around often and so I can strongly recommended it for fans of horror, sci-fi and mystery (even though it is none of those things!).