Books with new character options are my favorite type of rpg supplement. People sometimes call them "bloat," but I always found that term uncharitable. These kind of books let you build more specific, more esoteric characters, fleshing out the corners of the setting and suggesting entirely new campaign models. You want to be a Messenger? Suddenly a long, message delivery arc is possible.
The Adept's Journey: Mystic Paths doesn't just give you new Talents, Knacks, and Disciplines (although it has some of each), but rather it introduces an entirely new character advancement mechanic. The titular "Paths" are kind of like sub-classes, separate from your chosen Discipline. You can be a Scout-Messenger or a Troubador Messenger or a Thief Messenger, and the only real difference is which of the unlocked Messenger Talents you'd want to specialize in. Some Paths synergize best with specific Disciplines, but you're never actually locked out. It's a smart move that gives the book more versatility than, say, a collection of d20 prestige classes. You can use the bulk of it in any campaign, regardless of your party composition, and there's no real downside to the entire party choosing the same Path. Want to recreate 2e's "Horror Stalker Crusade?" You can.
The only thing that even slightly bugs me is Earthdawn's broader pattern of reify its mechanics. And it's not even really a problem that there are in-setting magical paths that grant, say, superhuman powers of scholarship and research. But why do the names have to be so incredibly on-the-nose? Many of the Paths are just named after the thing they do. Sometimes, this works out okay. Horror Stalker, Liberator, Purifier - these are, technically, abstract descriptions of an activity that don't imply the existence of a particular group, but they're esoteric enough that they can at least seem like proper nouns. No one's going around purifying things with mundane methods to such a degree that they start identifying as a purifier. It's not an ambiguity that will often need clearing up "oh, no, I see the confusion - I'm a purifier, not a Purifier. Can you hear the capital letter?"
But Scholars? Messengers? I guess this is just an aesthetic you have to get used to when you're playing Earthdawn. The Disciplines are the same way - you follow the ancient occult tradition of "Warrior" or "Thief," with no further clarifying details.
I think the main difference between generic-sounding Paths and generic-sounding Disciplines is that, at least in theory, you can pretend the Disciplines are simply game mechanics. The Paths are explicitly social organizations. You have to swear a blood oath to join one.
With the caveat that I think the Scholars should probably be "The Scholars of the Great Library" or something, I can say that I find all of the example Paths to be pretty interesting. The Messengers are playing with fire, being both a politically neutral mail delivery service and an anti-Theran espionage organization, but playing with fire is a great way to start a campaign, so I'm on board. Similarly the Horror Stalkers, the Purifiers, and the Liberators all have great built-in pitches.
Some, like the Fire Eaters, the Tail Dancers, or the Brotherhood of the Stone lack a specific campaign role, but are specific enough to enrich the setting. I especially like the Fire Eaters, because they take the game's boldest idea - that orks have an entirely non-human emotion called "gahad" - and turn it into a personal spiritual journey (plus you can set people on fire with your suppressed rage).
The closest thing the book has to a dud is the Journeyman path. And it's not really that it's a bad path. It's just confusingly named - "journeyman" already has a meaning in Earthdawn system jargon, being the second tier of abilities after PCs graduate from Novice (and because I know from experience that your first instinct is going to be to ask - no, the "Journeyman" Talent is not a Journeyman Talent, it's actually a Master-tier Talent). It's other flaw is that it builds off one of the setting's weakest bits of lore. Journeyman is the human-specific Path and it allows its followers to learn any Talents they like, because humanity's shtick is that they are "versatile." The ultimate Journeyman Talent (which is actually a Master Talent) is "Morphism," which allows the Journeyman to do some minor shapeshifting to gain the other races' special abilities and attribute modifiers. It's kind of interesting, in that by the old Shadowrun lore all the humanoid fantasy creatures were actually mutated humans, and thus you can infer that humans must have a unique potential for these kinds of transformations, but nothing else about the Path suggests that it plays off humans' unique role as the progenitor species, so it's really just kind of a weird choice. A shapeshifting power in a magical tradition that is otherwise not about shapeshifting.
Overall, though, this is just a fun grab-bag of Earthdawn ideas. There's something like 150 pages of new Talents and Knacks, a whole Discipline's worth of new spells, new spirits, new equipment, and that's on top of the setting-expanding fiction that comes with each of the Paths. It's definitely going to see a lot of use if I ever run an Earthdawn campaign.
Ukss Contribution: The Shaman Discipline (which seemed more or less inoffensive to me, even if I couldn't entirely figure out its cultural niche in Barsaive) has a couple of spells that involve cooking a big meal for the party and granting them buffs based on how many people are eating said meal. I like that. It's a nice, earthy aesthetic for a magic using class, creating miracles based on a wholesome domestic task and it's role in a shared community. Ukss will therefor have some form of magical cooking.