Oh, FFS (spoilers)
I'm not going to say I didn't like this movie. I did. I liked the performances. I liked the way they built up tension. I liked a lot of things. I even bought what they were selling me in the beginning.
But in all this time, with all the precautions they've learn to take, with all the research they've done (finding out how many monsters there are, finding out their habits, puzzling over how to kill them, etc.), it never occurred to them to try a simple shotgun to the face?
Why did they have the guns, then?
The entire sequence of events in the movie never even had to occur. I've hardly ever felt so cheated by a story.