Bought and read through the book. The lore pieces of the book (>50% of the pages) are excellent as we expect from Keith, he really gets into things like the nature of magic.
The mechanics are pretty heavily from Ruty, to the point that a few of the subclasses (College of Keys for example) are reprints from a previous product (Xanatha's Lost Notes to Everything Else). Given that subclasses are what draw a lot of attention, it's important that these are balanced. Unfortunately, most of them don't feel like they're contributing unique *Eberron* flavor, compared to the various PrCs in 3.5 supplements. The most flavorful of the subclasses, the Bone Knight (originally a PrC in Five Nations) has major balance issues. In addition to being a third caster pulling from the Cleric spell list, the Bone Knight gets *majorly powerful* features - free skeleton and skeletal warhorse companion, with the skeleton upgrading to a dread skeleton at level 10. What's worse is the dread skeleton, a non-MM monster, doesn't have so much as a *pointer* to where you can find it, let alone reprinting the stats as they're supposed to. The later features aren't that much better than eldritch knight, but for something that was supposed to be a highlight of the book I'm disappointed more development time wasn't spent on getting it to a reasonable level.
The other subclass that stands out as a mess is the Host Warlock, which breaks all sorts of 5e design standards in a confusing take on symbiotes. While I like the flavor (even if I consider the symbiote/graft emphasis of Magic of Eberron one of the weirder things in the setting), the execution just isn't there.
There's a few "alternate class options" sidebars, most of which are reasonable, but the Silverbow is just egregious. A divine variant on the Arcane Archer, the Silverbow gets a hilariously overpowered stunning+2d6 radiant arrow option. THe base Arcane Archer only gets blind+2d6 necrotic as its equivalent, a much worse proposition.
For the Races section, the (sub)races themselves are both flavorful and balanced. However, the halfling section brings back some old favorite unique halfling weapons as hideously complex designs, oozing with 3.5 weapon design. One clever highlight is the "Children of Khyber" section, which allows a character to start with an aberrant mark. Rather than making an aberrant mark subrace for every race, there's an aberrant mark race with each subrace representing human or dwarf or elf or...
For Feats, they establish some racial feats that would fit right in with anything out of XGTE. The fledgeling dragonmarks allow a character to develop a dragonmark post-character-creation, however I'm not sure that's totally necessary. I had a PC who wanted to develop their mark of making mid-campaign, and it was easy enough for them to just swap from Vuman to Mark of Making in a small rebuild. The advantage of just rebuilding is it means you're not stuck waiting for 4/8/etc. to make this important story transition.
The most disappointing chunk of the feats section is the Siberys marks, which are a power level mess (Mark of detection is *really* good, Mark of Shadows isn't), a history mess (Mark of Passage iconically got access to Teleport at the Siberys level. Now, it's... Another casting of Teleportation Circle, redundant with the greater mark?), a design mess (Why do Scribing and Cannith get a weird bonus to social rolls with other dragonmarks and dragons?), and an editing mess (any of the siberys marks that improve the associated intuition die). Given that this was supposed to be one of the "big pieces" of the book when Ruty and Keith advertised/described it, I'm rather disappointed.
The last two chapters felt like a waste to me - the advice on noir campaigns is eh, and the level 0 rules just don't have any place in 5e, where level 1 characters already die to a stif fwind.
Overall, a 3/5 product - the mechanics are a 2/5, the lore is a 4/5 (-1 for Dragonforged and the weirdness of the Mark of Death section, plus the last two chapters being ???). Fortunately, Ruty has indicated that they will be taking feedback and issuing a revision in a month, which will hopefully fix all the mechanical issues.
