Now, to rip it apart.
No, just kidding. The only real "flaw" of this book is that it reads like an accidental Pendragon supplement. Which comes as no surprise, since D&D paladins are basically Arthurian knights with the serial numbers filed off. It just makes it a little awkward when the setting they are clearly talking about is the County of Cornwall in Mythic Britain, but they have to pretend that they are being generic.
At times I wanted to scream "CHRISTIANITY! The think you're talking about is Christianity. That's the element that ties this all together." Honestly, the book is a little incoherent without it, and as a result can sometimes find itself flailing with the idea the Paladins are feudal knights, but not really because they are, by definition, servants of "Lawful Good," and so their main source of inspiration only lines up with AD&D's anachronistic cosmopolitan polytheist fantasy but coincidentally.
However, I want to make clear that The Complete Paladin's Handbook is the first book of this series that I would unreservedly describe as "good." Like The Complete Wizard's Handbook, it's undermined by the implicit setting assumptions that stem from AD&D's patched-together mechanics, but the Wizard book was also, on top of that, kind of a crummy book. With the possible exception of the Witch kit, it didn't really seem to know what people liked about wizards or understand the variety of mystic archetypes the class was capable of.
This book doesn't have that problem. It knows what it's on about, and it sells the Paladin class very effectively. So effectively, in fact, that you can see where it strains against the limits of AD&D's rules.
There are two main culprits here. The first is AD&D's unnecessarily specific strictures about the Paladin's wealth and associates. I've talked before about how AD&D 2nd edition awkwardly straddles a shift in the way rpgs are played (not my idea, but one I find convincing). This is especially apparent here. The Complete Paladin's Handbook wants to talk about things like character motivation and the way their relationship with their faith shapes the world around them, but sometimes it gets stuck having to reconcile itself with early AD&D's paranoid style of antagonistic gamesmanship.
For example, this is a thing:
To ensure that a paladin stays within his limit, it's important to clarify who owns each of the party's magical items. In general, a paladin won't use a magical item unless it is his [. . .]Um, actually, the spirit of these rules is that a paladin has a mind elevated above base concerns like the pursuit of worldly wealth and thus does not horde treasure beyond what's necessary to see to their needs and the effective pursuit of their mission. The idea that this translates into exactly 10 magical items at all times and under all circumstances is . . . well, it's nothing. It's an artifact of a system that assumes that players are only choosing the Paladin class as a pretext for cool, holy-themed powers and that they can't be trusted to roleplay their characters in a consistent way, so you've got to put an exact number on it.
Conversely, if a paladin has 10 items, he won't borrow items from other characters. A paladin won't look for ambiguities to exploit; he remains true to the spirit as well as the letter of these rules.
If, say, a Paladin was in the middle of clearing out a monster-infested dungeon and found a cache of 11 healing potions, it would be in the spirit of their oath to pack them all up and use them as needed, donating the remaining potions to a worthy charity once the monsters were driven off and the town was out of danger. However, that would violate the letter of their oath because each potion counts separately as one magic item, and so even if the Paladin started with only mundane equipment, they would have to preemptively designate one of those potions off-limits and not use it even if drinking the potion meant the difference between victory and defeat.
Which brings us nicely to the second of the two culprits - D&D's alignment system. It's bad. That is all.
No? Sigh. Okay.
The thing that makes Paladins such a great character class is that they are knights who walk the walk. All that stuff about truth, justice, valor, mercy, and charity? They actually believe it. A Paladin's natural foil, then, is a hierarchy that does not (and, in your more thoughtful works, cannot) live up to their standard. And yet so much of this book revolves around policing the Lawful Good alignment, as if that were an objective thing that could be measured and taken into account. As if feudal governance itself weren't a deeply flawed system that perpetuates routine cruelties to sustain itself. As if "all of your hirelings must be of Lawful Good alignment" doesn't become absurd when you're talking about setting up morality traps for the guy you've hired to do the tile in your castle.
The book is pretty clear. A Paladin must renounce their allegiance if the organization they serve ever stops being Lawful Good, but it elides the most interesting questions of the Paladin's condition - like, how would they even know? Maybe the deep corruption of the organization is offset by good members, like the Paladin. Maybe the organization is corrupt, but still generally does good work, or at least allows the Paladin to do better work than they could do alone. Maybe it still ostensibly stands for Lawful Good ideals, and could be reformed. Maybe a public break with a trusted organization, even if it has become corrupt, could undermine the public's trust in Lawful Good ideals. Maybe destroying the organization would cause more harm than letting its corruption continue? Maybe it's all those things at once.
A pretty interesting situation for a Paladin to be in, no? Unfortunately, Lawful Good is a thing with very clear and precise boundaries which can be detected with Paladin magic, so, eh?
The book never quite squares the desire to place a Paladin into a realistic feudal context with the fact that the D&D rules mean that a truly feudal Paladin should lose their powers almost instantly. Like, for all that it talks about Paladins shunning excess wealth, it also talks about them maintaining the accoutrements of the gentry and attending aristocratic galas. Which would be fine if AD&D were the sort of game that could let boundaries blur, but it isn't, and the book never quite forgets that it isn't.
The result is a book that is mostly very good, with only the occasional total absurdity.
UKSS Contribution: This one was a nail-biter, because its genre was barely D&D, and even less Ukss. I was worried I'd have to make another major compromise. Luckily, something came along that did not simply allow me to avoid incorporating chivalrous romance, but which I would probably have unironically chosen regardless of any genre concerns.
The Barding of Aerial Excellence. You put this armor on your horse, say the command word, and suddenly your destrier has sprouted 20-foot span metal wings! Take to the skies on a techno-organic fusion of horse and technology you wonderful religious fanatic, you!