Insultingly dumb movie
Four guys, four girls, one mountain-climber-turned-psychopath who for some reason is hell-bent on "proving" a person in danger will kill their friends to save themselves, even though his situation and their situations are not even remotely similar.
These people are supposed to be the best of friends, a tight unit comprised of college roommates, boyfriends, girlfriends, and the odd girl out -- the stepsister. Why would these people turn on each other?
We're not talking about a split-second decision here while a fraying rope is about to snap -- we're talking about people who have at least six hours to sit there and ponder the possibility of killing each other, or come up with a plan to overwhelm the one guy who wants them to turn on each other.
It's one thing to have characters die in brutal ways for the sake of a horror movie, it's another thing for characters to do spectacularly stupid things to make it easy for the killer to succeed.
This is not rocket science:
1) Get everyone into a bathroom with no windows, sweep it for cameras, then turn on the shower and sink at full blast so the killer cannot overhear anything, even if he's got the room bugged. (Clearly he had at least the living room and other common areas bugged.)
2) Find out who's being emotional or trying to be the hero, smack them in the face, and tell them they have no option other than to shut up, listen, and follow instructions.
3) Punch fatty in the face as many times as it takes to get him to shut up. Knock him out if need be. The point is, he needs to be stopped and cannot be relied on, and his panic is causing discord and harming the rest of the group. He has to be stopped or taken out of the equation.
4) Figure out a way to flush out the killer. This is NOT difficult at all. Send someone toward the van and/or motorcycle, force the killer to reveal his position by taking warning shots, and flank him. You have a gun. Give it to the person who is going to flank him. You already know the killer will take warning shots first, as demonstrated earlier.
5) Subdue the killer. Shoot him if you have to. Do whatever you have to do to extract information about traps, disabled vehicles, etc. Drag him to his own bear trap and offer to introduce him to his friend if necessary until he provides all the information.
6) Tie up the killer, put him in the back of the van, and drive to the nearest police station.
End of.
Again, it's one thing to pen a solid horror movie, and it's another thing to write a script that requires characters to shut down their brains because you couldn't think of a better way for the killer to operate.