The Player's Guide to Eberron (James Wyatt, Keith Baker, Luke Johnson, Stan!) has the sort of format that paradoxically either makes me read really fast or makes me read really slow. It's divided into a series of encyclopedia-like entries that are all some precise multiple of two pages long. So I can either finish a section quickly and say to myself "this seems like a natural stopping point, I'll just take a little break" (followed by four hours of video games) or I can finish a section quickly and say, "wow, that was easy, I'll just do another one right away." There's no middle ground between these two reactions, but each one is equally likely.
The real tie-breaker in these situations is how interesting I find the subject matter. And in this case, I found the subject matter very interesting indeed . . . but like 85% of it I've already seen before. This book calls itself a "player's guide," but it's not clear to what end it's meant to guide players towards. Like, maybe it's just the case that players empirically don't read core books (let alone supplements) so they tried to manifest a similar outcome by giving a player-oriented title to a condensed lore compendium. The same thing happened in Planescape with the Planeswalker's Handbook.
Also, frustratingly, like the Planeswalker's Handbook, the Player's Guide to Eberron is probably the best entry point into the series. It's a broad cross-section of things you need to know about the world of Eberron, but just enough that you can pluck each individual topic out of context and be done with it in a couple of minutes. You want to play a warforged, you turn to the "warforged" section near the end (they're arranged alphabetically, like an encyclopedia) and you get a bit of information from the main campaign book, a bit of information from Races of Eberron, and maybe a very little bit of information from the adventures and it's all very functional. But it doesn't actually tell you how to build a warforged character, and only offers two extra feats, so you still actually need the main book. I guess that means that the Player's Guide to Eberron is meant for people who have all the other books . . . but don't read them?
This is not as off-the-wall a theory as you might suppose. There is some novel information here - three new prestige classes, a bunch of new feats, a couple of new organizations - but the bulk of the stuff that expands the actual Eberron setting comes in the form of references to things you'd originally find in various non-Eberron D&D supplements. Want to know how to play a xeph or a raptoran? How to incorporate Magic of the Incarnum into the setting? There's a sidebar for that. I've heard it said that "if it exists in D&D, it has a place in Eberron" and this book here is the proof that they at least put some thought into fulfilling that promise. Most of these little cameos feel like an afterthought, but afterthoughts are a kind of thought, so I think it's fair to say that Eberron has earned the right to call itself a kitchen-sink setting.
I wouldn't necessarily call it a satisfying sort of kitchen-sink worldbuilding, however. It's very uneven in the degree to which all of these disparate elements are given something significant and cool to do. Incarnum magic is largely confined to The Island Where They Do Incarnum, the thri-kreen "wander the wastes, though they are hardly numerous," and yeah, it turns out that the various nations of Khorvaire have militant philosophical organizations that resemble the Samurai class. On the other hand, the Elan get a cool new backstory (they are living prisons that trap quori spirits deemed criminal by the Dreaming Dark - the spirits are forced to possess the body, but bound to have no control over its actions, and the composite creature is an ageless, psionically-active being with no memory of its previous life), the shujenja class represents the priests of a dragon-worshipping religion, and swashbucklers are so integrated into the themes and aesthetics of the setting that they're barely worthy of comment (in a good way).
I'm in the unusual, though likely not unprecedented position of having read every Eberron book published thus far and most of mainline D&D books being referenced in the sidebars. I've got very close to maximum context (somewhere between 92% and 95%, I'd say) and what the Player's Guide to Everron feels like to me is a bunch of old-hat information sprinkled through with trifling little tidbits. On the one hand, I'm not necessarily opposed to the old hat per se, and I absolutely live for little tidbits, but on the other hand I'm hard-pressed to imagine a significant use for this thing. A book where they went through all of 3.X edition's obscure sourcebook and gave me a paragraph of canonical Eberron backstory for every random prestige class and monster with an Int score would likely be one of my all-time favorite rpg supplements (period), but wedding a partial implementation of that idea to a rather unambitious recap of Eberron as it stood in January of 2006. . . well it commits the cardinal sin of kitchen-sink worldbuilding: it doesn't make space for the new material by making the world feel bigger. Rather, the boundaries of Eberron feel very similar to what was established in the main campaign book, and it's just the margins that feel a little bit more crowded.
I have a certain experience with this very tension in the world of Ukss. It's easy to just keep adding new stuff without any regard for what has come before, and at the start it can feel like an expansive bigness, but if you don't make the effort to fit the pieces together, the whole thing can become so expansive that it loses coherence. New elements can't just be for the gaps, because that's making the new stuff subordinate to the old, but if you're always making room for the new elements, that's just the same problem seen from the other side. You need both an openness to expanding the horizons of the possible and a dedication to finding connections between your ideas and fitting them all into a single context. That's hard enough when you're scrupulously curating everything to go into the melting pot. I shudder to think of how it might feel to just inherit all of D&D's vast and sprawling canon all at once (oh, the writers of Races of the Wild thought it'd be cute to have catfolk . . . they can live in the jungles of Xen'drik, I guess).
Overall, I'd say that I have no strong feelings one way or another about the Player's Guide to Eberron. I like Eberron as a whole . . . and this is certainly Eberron, all right.
Ukss Contribution: One of the critical pieces of technology in the world of Eberron is Khyber dragonshards. Arcanists use these crystals to bind elemental spirits into the locomotive systems of airships and rail carts and a bunch of other useful items. These crystals are found, naturally occurring, in the vast system of caves that is Eberron's equivalent to the Underdark.
The Ukss contribution for this book is a weird bit of trivia about these Kyber crystal deposits - that sometimes they will randomly ensnare passing demons. Obviously, this is mainly meant as a cool hazard for dungeon-delving adventurers, but I can't help looking at this phenomenon from the perspective of the demons. A slight, but not insignificant danger to wandering around underground is that you might get trapped in some bullshit rock. I find the cultural implications to be fascinating.
