Knowing nothing about this before I turned it on, I assumed from the description that it was going to be some sort of "Predator" type deal... two snipers trying to evade an extraterrestrial threat. The opening scene was promising, leading me to think that it was going more for a supernatural vibe. Then it morphs into a reasonably entertaining action (sort of) flick about a mission gone bad. I was thinking of that old movie with Owen Wilson as a downed pilot behind enemy lines trying to get back to safety (Behind Enemy Lines). He was being pursued by a determined sniper, and I thought this movie was going there too. I really liked the idea that the sniper hunting them was a woman. Then it returns to the Predator/supernatural element. The final scenes suddenly make it clear that it's about PTSD. In fact, the director hammers the viewer over the head to get the point across. My complaints:

1. These two guys were black ops snipers who did in-and-out operations. Why would the main character be suffering from PTSD? It's not like they were in a conflict zone experiencing fire fights, explosions, suicide bombers, etc on a daily basis. It seemed like every few weeks they were sent off on a bag-'em-and-tag-'em mission... stressful, yes, but enough to produce full-blown PTSD? I was dubious. Yes, this mission goes bad and they find themselves being hunted by enemy snipers, but it's nothing that they shouldn't have expected or been trained for.
2. I guess we're supposed to understand that the creature hunting them was a manifestation of the PTSD. But why did the second man -- initially disbelieving -- suddenly start seeing the creature too? I found a stretch that both men should suddenly fall off the cliff near simultaneously. We later see the creature behead him in third person view which would imply the creature was physically real.
3. Did the female sniper see the creature as well? She sees Bryant start yelling at something, pans over to see what he's talking to, troubled look on her face, she simply leaves without shooting him... Did she see it, or did she just assume that he had lost his sh!t and decided it wasn't worth killing him?
4. They kill an innocent man which causes a lot of distress for one of them. They should know that collateral damage is a likely outcome of these sorts of missions. And did they even kill him? The closing scene was of the old man sitting at the window. Flashback? A big hint that the PTSD was triggered by guilt?

It was a promising movie, but I think the director made things a little too obtuse initially, then a little too obvious at the end.