The subject is a good one, but Bill Maher doesn't have much depth here, and is often punching blindly.
Something like this documentary could be --and should be--done by someone with a better understanding of the subjects, their histories (how the religions evolved) and perhaps a more thoughtful introspection of WHY people want, and nurture faith.
I mean, sure, preposterous supernatural stories are just fun to poke at, but if the explanation is supernatural, the preposterous nature of the story kinda goes with the territory.
I find it funny that most of the criticism about this revolves around it being "biased", as I don't think there are many documentaries about religion that aren't biased.
By and large what makes this movie so 'meh' is it is rarely informative and it isn't all that entertaining. While some of his foils come off as real jerks, others come off as punching bags ill-equipped to deal with Maher's professional snark.
Bill's "personal journey" isn't all that interesting and for something that seems to be at the central core of the movie is hardly considered with any real examination.
As a comedian Bill is a bit of a one trick pony, he favors mockery and put-down rather than some of the angles that makes comedy one of the greatest arts of shedding light on subjects.
I think the tactic of the atheist going after the low-hanging fruit of the unbelievable story is almost always a losing venture. Calling someone's religious narrative "fairy tales" may very well be 100% accurate, but more often than not makes the believer defensive and prone to shut the door on discussion. Yeah, it's true, but sound hostile.
I think the best angle for discussion is going after the very nature of faith itself. Why is faith good? Can faith be questioned? How far does one take faith, and why? Why is your strong faith in X any different than someone elses's faith in Y? What happens when faith confronts a compelling reality that refutes it?