The Everlasting Man was one of the toughest to get through. Written as a rebuttal to H.G. Wells An Outline of History, Chesterton wrote the book to refute the idea that man is merely a part of the animal kingdom and that Jesus Christ was just an influential teacher.
Unfortunately the first half on the development of man and religion is quite a slog. If you can hang on until the chapter on the incarnation, "God in the Cave," you will be richly rewarded with G.K.'s insights into the first Christmas. Some of it is simply astonishing. He talks of Christ's birth as a cataclysmic event of good against evil.
Unless we understand the presence of that Enemy, we shall not only miss the point of Christianity, but even miss the point of Christmas. Its unique note is the simultaneous striking of many notes: of humility, of gaiety, of gratitude, of mystical fear, but also of vigilance and drama. There is something defiant in it also; something that makes the abrupt bells at midnight sound like the great guns of a battle that has just been won.
I had heard that this book was instrumental to C.S. Lewis' conversion so I read it looking for clues as to influential passages. Certainly "The Riddle of the Gospel" contained ideas that Lewis would later make famous in his Mere Christianity.
In the chapter on "The Witness of Heretics," Chesterton defends unchangeable biblical truth. What the denouncer of dogma really means is not that dogma is bad, but rather that dogma is too good to be true. Dogma gives man too much freedom when it permits him to fall. Dogma gives even God too much freedom when it permits Him to die. To them it is like believing in fairyland to believe in such freedom as we enjoy. It is like believing in men with wings to entertain the fancy of men with wills.
I can't recommend this unequivocally because it is a lot of plain, hard work, but if you like Chesterton, this would be a worthwhile effort. (In the future I will probably re-read just the second half!)