Great film
This is an incredibly well executed film from start to finish. The unease slowly builds to an almost unbearable level that pays off with the brutal truth of what was really going on.
You really feel like you're in the mindset of the main protagonist throughout. You feel his paranoia, grief and self doubt. The ending avoids getting silly too which I love. I was waiting for that cliche of a bad guy supposedly being mortally wounded and then surprising everyone by jumping up for one last attempt at carnage. I'm so glad they avoided that. I thought the little red lamp twist at the end was effective too.