I have seen that this book is intended for the younger among us, though I'm about 15 years out from Sir Able when he first entered into Mythgarthr, I will attempt to speak of it to inform that audience of my thoughts.
I... did not like or love this book. At times I enjoyed it, or found particular scenes, vistas, character expressions, and so on, to be moving, I had a number of gripes. Wolfe's prose is delightful, his willingness to use the Seven Realms to emphasize who/what is more or less *real*, I enjoyed greatly. I thought he used the world he built tastefully, and though I'm certain I missed many facets and details, I appreciate his willingness to allow us to miss things. This is a book that rewards some careful consideration in between chapters, if put down often enough. ((Which I did, although because the book frustrated me, until I had no option but to read this or stare at a wall, at which point I finished readily.))
My ultimate issue is with Wolfe's chosen protagonist, Sir Able of the High Heart. He is just... utterly uninteresting. Anything he is not immediately good at, he approaches with perfect humility until he is good at it. Brief tangent, I think the decision to report the book as a letter to his brother did the story a number of disservices. Perhaps Wolfe thought that it might emphasize that Sir Able's experiences were mythical and hard to put upon the page, but it frequently robbed the story of tension and emotion. His forgetfulness of any events does not color him as a protagonist later in the story.
He faces no emotional struggle from his life in America overlapping with his life in the given setting. He is not afraid, he does not make mistakes that cause him any real difficulty. If he does, the mistake was actually a good thing and he is rewarded or gets yet another servant or slave. He is simply fated to become a knight, accepts this as fact, and does it. He's a boring ol' Chosen One. He rarely, if ever, acts rashly. He rarely, if ever, acts like a teenager. He never for a moment doubts that what is happening in front of him is real. I think this lack of emotional weight might explain other reviewers' feeling that things just kind of happen haphazardly in this story. That is, there isn't much a sense of buildup and release, at least not consistently in a way one might expect. What Sir Able chooses to emphasize or de-emphasize in his telling is often jarring, such as participating in a tournament to win an audience with King Arnthor is told in like, two pages. Anything he does not understand is usually explained by his unfamiliarity with Mythgarthr, not his youth, despite his constant refrains that he's but a boy.
When I think of the kind of knight I would like to be, I would have little in common with Sir Able.
It is interesting that Sir Able is willing to use certain unconventional methods to assure victory, such as "befriending" aelfs and ogres and such, but again, this isn't something that chafes with his expectations of knighthood or others' perspective of him. A certain character in Sir Able's employ is frequently a trouble maker, but it doesn't matter, even when that character eats people. If Wolfe wanted an unreliable narrator whose perspective colored the tale more thoroughly, I would point to Till We Have Faces by C. S. Lewis as something I read recently. That, too, is a fantastical story written as though in a journal, but implements it far more effectively, in my opinion. It doesn't do so in a way that compromises tension or the incredible insanity of that protagonist, or the weight it imposes. The flaws in her storytelling become clear and later collapse around her, whereas, even when Sir Able claims he is not able to fully report something, or saves something for later, it never retroactively 'destroys' anything. This claim may be false, but I doubt I'll be re-reading this anytime soon to go and check.
Sir Able is not particularly kind, or particularly clever, or particularly skilled. His greatest strength, it would seem, is that he adapts quickly, rolls with the punches, and risks himself for advantages, which he does frequently and never with any lasting consequences. He'll often deck someone because they doubted his knighthood ((at least in The Knight, not so much in The Wizard)), offer them his services as payment for decking them, and then get what he wanted with no trouble at all.
He is frequently tempted by various supernaturally hot women, and occasionally indulges in a kiss or two, but never cracks, never relents, for his is already forsworn to the Queen who knighted him in the opening pages.
You know, as a teenager, I wanted to believe I could slay dragons. I have slain one or two in my time, but it never, ever, was so easy as Sir Able made it look. That is, perhaps, the caution I wish to give to anyone in their teens, or younger, reading this. This is just... not a thoughtful representation of what could be going through the minds of the young. Maybe I just haven't been a teenager for too long, but I think even at that time I might have found something off. There are many ways in which Wolfe respects his reader greatly, for which I *do* think such a book might be delightful.
If you like a tale of someone winning, making cool friends (although they're more frequently better described as 'assets'), and generally earning for themselves status as a legend of the realm, you'll enjoy this. But, if you want emotionally complicated characters, you will not find that here. Sir Able, the unwavering heart of this story, can do no lasting wrong, and it's as if everyone in this story knows it. Everyone loves him after five minutes, and it's just so fucking boring.