Sometimes, when a movie has a interesting idea, it doesn't always deliver (I'm looking at you The Platform).
Well, this movie absolutely deliveres with a good concept and a fairly good plot.
It has it's flaws, like being a little predictable and the characters could've made smarter decisions, although we didn't had a movie of they did. Sometimes, you need to something stupid to have a story you know?
Good thriller, watch it if you can.