At its core, the film is about the debate between those who believe that the bible should be taken literally and those who believe the bible should be read in the light of the times and cultures in which it was written.
As a movie-going experience, I found "FTBTMS" reasonably compelling if condescending at times. Most of the featured individuals and families had interesting stories to tell -- perhaps most notably Episcopal Bishop Gene Robinson of New Hampshire who is a gay man in a committed relationship.
But, the film had a clear predisposition against those who belive in biblical literalism. Most of those who agreed with the filmmakers' point of view were shown in a positive light. Those who disagreed were mostly represented poorly, including by the likes of tele-evangelist Jim Bakker. Anyone hoping for a balanced analysis of the question would have left the theater disappointed.
The filmmakers also neglected to examine Catholic teachings on the topic in favor of a concentration on Evangelical viewpoints. Despite being the largest Christian denomination in the United States at some 60 million faithful, no leading Catholic on either side of the debate was presented. Sorry, Chrissy Gephardt doesn't cut it for me as the lone Catholic voice on the question.