I would, on the whole, agree with the review by "filthmonkey" below. At times Humphries shows very clearly that he has made a concerted effort to try to understand religion (Christianity moreso than others, for obvious reasons), and yet at other times he stumbles into tired old misunderstandings that one finds hard to believe someone hasn't corrected him on at some stage in his search - such as the idea that for most of history it would have been tantamount to a death sentence to admit you didn't believe in God.
The interviews are enlightening, not because they present the overall arguments of the various religions represented, but because they show that when it comes to faith there are no experts or teachers, only people telling you what they think. Their ideas may be informed by a wealth of theology, cleverly strung-together arguments and historical perspectives, but there's still nothing concrete. All there is left is "just believe", or "you just have to take in on faith".
The book dips a little in part six, on consience, when he misses the point by the bucketload. He somehow manages to seamlessly move from the question of whether objective morality can exist in the absence of God to the question of whether it's possible to be 'good' without God, and treat them as if they are the same question. He makes the time-honoured error of bringing up the Crusades, Inquisitions and Witchunts as unmitigates crimes of religion without showing any understanding of the historical facts and complexities of these events. He also mistakenly changes Sam Harris' surname to 'Smith' (four times no less), albeit whilst making a very cogent point. (Maybe this has been or will be corrected in subsequent editions...I've read the paperback.)
I disagree with some reviewers that Humphries is disproportionately critical of 'militant atheists'. He chides believers for their weak arguments, and some atheists for assuming an intellectual superiority.
But overall, what he does WELL is to show how an intelligent, rational, yet at the same time genuine and open-minded person can either lose or fail to find faith in the first place, and also show that the confession of faith is not at all symptomatic of stupidity (a fallacy which he identifies as "the core of much atheist polemic"). It's also hard not to agree with him that the most important question is what allows one person to have faith, and another person not.