A lot of people tend to say that the characters were boring, and one-sided, and didn't have much going for them. I would say that's exactly what the film wanted to portray. You are put into a situation much like what the characters are going through.
To put yourself in a situation where you have nothing to do, and are bored out of your mind, would make anyone go a bit crazy, including the audience. Not everything has to be filled with crazy unrealistic scenarios where they start killing each other. It was definitely a realistic, slow-burn film.
I think the movie is very thought-provoking. I found it to be quite fascinating with the character development. You can really see someone's true colours if put into the right circumstances.