It's an interesting book, though I cannot say I felt like "stout Cortes" gazing with great amazement at the ocean the poet thought he saw, first among europeans. Chesteron was a clever fellow, and was far too intelligent to maintain that he was attempting to demonstrate why one should be a Christian. Instead he purports only to tell us why he is one, in an apparent effort to avoid being characterized as an apologist for the faith. He is careful to note of all his arguments, such as they are, that they address matters which can't be adequately expressed in words. In other words, he takes pains to cover his (reputedly enormous) ass as he goes about explaining his eventual acceptance of a truth which he seemingly believes cannot be verified, but which he claims was always there, awaiting discovery, much like the Pacific Ocean.
He writes that fairy tales (told to him by his nanny) played their part in his eventual acknowledgement of Christianity. He seems to have felt that they contain some truth beyond common sense. Perhaps this delight in fairy tales was typical among english gentlemen of his time. Not being one, however, and having merely read some of them as I had no nanny to tell me of them, I don't find them as impressive. One he doesn't mention is that of Goldilocks and the Three Bears, but I think that fairy tale in particular tells us much about why he became orthodox eventually, or at least how he explains he did so. After some time and having tried other ways of comprehending the world, he simply came to believe in Christianity because it feels "just right."
He seems to prefer proclaiming to explaining. There is not much in the way of reasoning to be found in this work. I'm not familiar with most of those he finds wanting in various respects, except Bernard Shaw and Nietzsche (he also mentions H.G. Wells as being lacking), and so can't say with any certainty whether his charcterizations of them and their opinions are fair. What he calls materialism, though, seems to be of a very simple-minded variety, and his criticisms of eastern religions, primarily Buddhism, may have their bases in what those religions appeared to be to the theosophists and other european mystics of that time. In other words, his criticisms, like his arguments, are cursory and conclusory. Being fond of the stoics, I thought his treatment of Marcus Aurelius was rather shabby. He seems to have believed Marcus to be less than manly in his approach to life. It seems inappropriate for an obese english gentleman of very comfortable means to take this view of a Roman Emperor who spent the bulk of his reign in military camps and campaigns against tribes such as the Quadi. As I recall, the dreadful C.S. Lewis felt that Christianity was the only truly "manly" religion as well. Perhaps Lewis had a nanny also.
His defense of the Trinity seems merely weird. If I understand him correctly, it somehow prevents us from viewing the Supreme Being as a kind of dictator, or from it being one. It is instead, through the mystery of the Trinity, a kind of unusual committee; Jesus the human humanizing the Father, and the Holy Ghost doing whatever it is supposed to be doing, in a kind of harmony. But, having heard the Trinity explained by a priest as analogous to a ham sandwhich, I can accept that Chesterton's view may be as good as it gets.
Regardless, I feel the same disappointment reading Chesterton on Christianity as I have felt reading the apologies, or explanations, of others concerning it. No real effort is made to explain the divinity of Christ, which would seem to me a fairly important aspect of the religion. Christ said remarkable things, says Chesterton, and if we can trust what others wrote regarding what he said that may well be true. It doesn't follow, though, that he was God. Regarding the fact that there were admirable humans long before Christ lived, this means, says Chesterton, that they were really Christian, but Christians who evidently were not required to know of Christ or believe him to be God in order to be Christian.
One wonders why the more sophisticated and intelligent defenders of Christianity spend so little time and effort on establishing why Christ is divine, or whether it is necessary to believe him divine in order to be Christian.