Opening Thoughts:
Per requests, I'll be tackling just one chapter at a time for the rest of this project, so I hope folks will find this easier. Despite "Faerieland" being a recurring feature in many European mythos and folktales, D&D has never done it very well before. TSR had the roaming Court of Faerie wandering around the Neutral Good/Chaotic Neutral corner of the upper planes, with hardly any attention paid to its existence even in its Planescape materials, whilst the best that 3e did was a single brief mention of the Plane of Faerie as an optional plane in its take on the Manual of the Planes splatbook, describing it as a realm filled with half-celestial and half-fiend fey creatures of all types to make up the Seelie and Unseelie courts.
The Land of Faerie:
Our chapter opens with a very short (half-page to third-page) description of what the Feywild is, with the rest of the space being taken up by the sidebar "The Underdark and the Feywild" (see the section "Birth of the Feydark" below) and a black and white depiction of the new dryad.
In short, the Feywild is the magical, fantastic reflection of the world; birthplace of the fey and home to many wondrous and unearthly beings, animals and beasts. An unintended echo of the mortal world that proved self-sustaining, it resembles a "canted" version of the world rather than a faithful reflection. The landscape seems similar enough, at a first glance, but distances are askew, and the wilderness dominates here, with civilization being rare.
Readers are instructed to put visions of happy magical woodland paradises ala Disney out of their heads; the Feywild is a dangerous twilight realm, a place of natural beauty charged with raw arcane essence, heightened beyond mortal experience. Oh, it can be welcoming and cheerful... but much more commonly it is dark, frightening, mysterious and outright hostile.
Similarly, the fey of the World Axis are a darker, wilder breed than their counterparts in the Great Wheel. There are no "inherently good" fey anymore; these are wild, even downright savage, and dangerous.
The Birth of the Feydark:
It was the existence of the Feywild, ironically, that resulted in the Underdark developing into a transitive plane in the World Axis, although they don't discuss that in depth here, sadly. Instead, this sidebar simply reveals what would later be explained in the Underdark sourcebook - that the Underdark lies beneath the Feywild as well as beneath the mortal world. Which only makes sense; as the sidebar itself admits, a lot of fairy stories depict them as living underground in hidden subterranean kingdoms, mentioning by name the Irish Sidhe and the Scandinavian Alfar.
It also notes that they considered moving the drow here, to better cement their rivalry with the eladrin, but they ultimately decided that making drow an extraplanar threat was too much of a change - instead, this locale was given to the fomorians, allowing the Scramjet team to more deeply draw on the Irish folklore from which those monsters came but never really lived up to in past editions.
Locations of Note:
The shortest subtopic in the chapter, this examines three sample locations; the famouse Isle of Dread, which has appeared in past editions as an adventure site; the Fortress of Mag Tureah, which is home to the lord of all the fomorians, and the Court of Stars, from whence King Oran and Queen Tiandra rule over all the fey of the Feywild.
Adding the Feywild to your Game:
Barely two paragraphs long, this subtopic discussess that the Feywild should, ideally, be every easily integrated into lone adventures or long-running campaigns, since it makes a strong impression but its native creatures run the whole gamut from low-level threats like pixies and boggles to epic-tier threats like archfey. In this, it's actually drawing from many real world medieval folk-tales, where people would frequently cross into the land of the fairies by simple accident.
Integral to the very nature of the Feywild is that you don't need fancy magical rituals to get there; hidden passages and portals are scattered in profusion around the known world. To quote the book: what seems to be a gigantic but abandoned ruin in the mortal realms may lead in to Mag Tureah for anyone brave or foolish enough to wander into its crumbling halls at night.
Elven Gods:
Another short sidebar, when summarized, this two-paragraph bar explains why the Seldarine of the Great Wheel was boiled down to a trinity in the World Axis; Corellon, Lolth and Sehanine, together, each represent one branch of the elven peoples - Corellon for the eladrin, Lolth for the drow, and Sehanine for the elves.
Eladrins:
Now we finally get something a little meatier, although I covered this sidebar in my 4e Race Review project for the Eladrin review...
This subchapter talks about why Eladrin, an elf-like race of outsiders who filled the "Chaotic Good Angel" niche back in the Great Wheel, were axed and their name taken for the newer, more distinctive version of High Elves. In short, because you can read the entry quoted with a longer writeup by me in the aforementioned review, the Great Wheel's take on eladrin were axed from the World Axis because they no longer served a necessary purpose in a cosmology not wrapped around the traditional alignment grid, and they simply weren't interesting enough to stand on their own, certainly not when they were competing with high elves for much of the same thematic space!
So, the decision was made to take the eladrin name, which would make the "three elven branches" more distinctive by having non-type based naming conventions, and double down on their "feyness" by mixing them into the high elf pot. Which, as I've said before, only makes sense because eladrin were basically TSR's attempt to do Sidhe/Seelie Fey.
Fomorians:
This subtopic is actualy divided into subtopics in the book proper; "Fomorians" discusses who the fomorians of the World Axis are from a flavor perspective. "Formorians Reconcepted" talks about the historical status of fomorians and how they were redesigned for the World Axis.
Let's start with the latter first, for context. As the author notes, traditionally, fomorians were kind of shafted. Far from the supernatural powerhouses of Irish Celtic folklore, the D&D fomorian was just a deformed, slightly smarter take on the hill giant - a malevolent, ugly brute that was only really good for smashing things. Their most interesting aspect was that they lacked a clear elemental connection like the vast majority of other true giants did. Then, during a Scramjet meeting, the topic came up: since "giant sized" and "Giant species" was to be no longer synonymous in 4e, then what about making fomorians into a Fey race? This idea caught on with the developers, because it tapped more firmly into the myths from which fomorians originated. With the decision to keep drow lurking in the depths below the mortal world, this also opened up a new niche for the fomorians; they became the "dark lords" of the Feydark, a wicked and powerful evil empire of physically and magically mighty faeries who rule over the various dark fey of the World Axis in their benighted underground kingdoms. They also came up with a new defining deformity for them; baleful distorted eyes imbued with dark magic, echoing both the common folkloric theme of the "Evil Eye" in general and the deadly killing gaze of the fomorian king Balor in particular. In their opinion, this gave fomorians a far greater role to play in the new cosmology than they'd ever had before, and made them much more compelling than their Great Wheel counterparts.
The flavor subtopic describes fomorians as giant-like in stature, but dark fey in every detail that counts. It calls them the largest and most powerful of a group of related dark fey races, collectively known as the Fomors, but I don't think this angle was ever maintained into mainstream 4e lore. All fomorians are uniquely deformed, with twisted features, tumorous growths, hunchbacks, distortedly over- or undersized limbs, and crooked bones being cited as examples, but all fomorians share one mutation in common. This mutation is the Evil Eye, an oversized, cat-like orb that causes its host constant pain, and often bears another magical curse, such as plaguing the host with nightmarish visions of the future, constant waking nightmares, or an inability to see the beauty in anything around them. As much as their evil eyes torment them, they are also the focus for their magical powers. Despite their brutish miens and propensity towards madness, fomorians are highly intelligent and naturally gifted in the use of magic. They surround themselves with beauty, in stark contrast to their own ugliness, and dwell in titanic, eerily beautiful Feydark kingdoms populated by evil fey. Whilst infighting is a frequent problem, they all turn their wrath outwards, seeking to conquer and subjugate new lands and victims, and for this reason are locked in perpetual war with the eladrin.
The Fey:
Finally, this chapter closes by examining what the goal was with the entire fey monster typing for the new cosmology. Similarly to how giants were reworked to take them away from their "big humans with some minor elemental trappings" characterization, the team wanted to move away from the... well, let's be honest: rather lackluster depiction of fey in editions past. Most fey in TSR's books tended to fall into one of two categories; vaguely elfish-looking pin-up fodder like nymphs and dryads, or generic good-aligned mischievously twee little people (pixies, sprites, leprechauns, brownies), etc. And 3e didn't really stray too far from this mold, either.
This wasn't good enough for the Scramjet design team. They wanted to go back to fairy-tales of old, pre-Disneyfication. To quote the book, they wanted to convey the terror of the Wild Hunt, the hopelessness of getting lost in a faerie mound, and the terrible horror that lurks in the original version of almost every Grimm's fairy tale.
So it was that fey became a much darker and edgier set of creatures. Though we're not given any details on how that applies in general, we are given one example to whet our appetite: a swarm of pixies. In the Great Wheel? A bunch of childish little mischief-makers. In the World Axis? A swarm of flying, tearing teeth that can quickly reduce a hapless adventurer to a pile of picked-clean bones.
Closing Thoughts:
I really love the Feywild. The influence from European fairy tales and Celtic myths from Scotland, Ireland and Britain is clear, but it doesn't feel like a simple repetition of any one real-world mythos. The Sidhe, the Seelie, the Alfar, they all have their place here on a conceptual level, and it feels so natural!
The fey have always felt like an afterthought in D&D. From AD&D and BECMI through to 3e, they've always just been there, but with no major presence in the greater cosmology. They exist because TSR felt obligated to do so, but there's no real incentive to use them, nor do they immediately suggest any major use for them. 4th edition was the first edition that really tried to actually give the fey a place and a reason; the Feywild is the fruit of their work, and that is why I love it so much.