speaking solely as a movie, i didn't really liked it. not because there were no FX or because we had a single cabin as the scenario for the whole film, actually that was what kept me watching it.
i didn't like it because the acting was shady, his "friends" are all happy and then they're mad, but you have no idea why; then they take distinct roles, one is the believer, other is the antagonist, but they never really make the point! also, the lighting was terrible and i'm just mentioning technical issues.
in a few words, i thing the movie could have just had a "ok i'm outta here!" from some characters. like the lady who doesn't want to hear his version of the bible.
about the story itself, everyone is free to write about what they want, and the story is proof of some good writing and imagination. i credit the book author for that, hence, my 4/10.
so, in the end, hear the man's story believe it or not, just don't spend the whole time acting like you believe him and being shocked at what he says, and at the same time moving around and making jokes like you don't believe him.
Coherence.
thanks for reading ;)