It sometimes feels like the goal of Masters of the Art is to persuade you not to play masters of the art. It doesn't do anything so obnoxious as warn you off directly, but its depiction of the adventures of those who have pushed beyond the limits of Mage's standard 5-rank Sphere system often borders on "you are constantly held in check by everything in the universe - good luck."
Not even a joke. "In general, the most common use of Archmagic is in corrective action: preventing serious magical mishaps from becoming any more destructive. When an Archmage derails the time line or drops a flaming mountain towards Earth, other Archmages are quick to rectify the situation." Even in a book that has rampaging space beasts, synthetic universes, and full-on D&D-style liches, the setting can sometimes feel oddly constrained.
Did you know it's a good idea for an archmage to try and hold down a job? Fool, my job is creating planets. I need to maintain relationships with Sleepers to maintain my perspective? Nobody's getting in my social circle unless they're a dragon, pagan god, or angel of Principality rank or higher. I mean, yes, I might lose perspective, but as a person who can break Time, maybe the most adaptive perspective for me is the view from the mountaintop.
Although, Masters of the Art doesn't really approve of that kind of swagger. It's very consistent in the position that what you should be seeking is "Ascension" (you know, like "Mage: the . . ."). It even says, at one point that "godhood isn't the reward it seems." So whatever Ascension is, you know it must be good. Though, honestly, the way they describe it makes it sound a lot like death. There's a brief fiction where someone ascends, and from the perspective of our universe, she just disappears, never to have any noticeable effect on anything ever again.
Maybe that's just the atheist in me talking, though. Despite what the books imply about the Order of Hermes and the Virtual Adepts, the defining element of the Traditions is that they are religions (it's actually a huge missed opportunity that none of the writers of this game appear to have heard of the Singularity, because it strikes me as the perfect tech-Tradition eschaton). To be a mage is to be on a religious journey, and an important element of that journey is the final destination - the state of eternal peace and ultimate enlightenment from which you never return because any change in your condition would be a diminishing of perfection. I.e. Ascension.
I, however, can't help but think that the penultimate bliss sounds like a better deal. Safety and comfort in a mode of existence I currently understand, combined with the freedom and resources to be constantly doing cool shit for as long I want. Masters of the Art would call that "straying from the path of enlightenment" or "succumbing to the temptations of power," but I can't help but think about how every example of Ascension we've seen so far (which is, admittedly, just two or three) has involved the enlightened leaving behind the people and things they love in this world and then being of precisely zero damned use to them for the rest of time.
There is a suggestion that there could possibly be a global Ascension, where everyone becomes enlightened all at once, but as an idea it's tarnished by being the Technocracy's plan. I think this is one of those things that might change in later books (the Celestial Chorus, especially, want a group Ascension), but for now individualism = good and collectivism = bad.
All that being said, Ascension does appear to be preferable to archmastery, if only because Masters of the Art makes the rank 6-9 spheres into an absolute mess.
At best, they're lower-level powers scaled up and absent guidelines for their proper use. How many successes does it take to move a continent with Forces 7? Does the size of the continent matter? Can you move Europe separately from Asia or is that whole landmass a single unit?
At worst, the powers are so esoteric that it's hard to imagine a situation where you'd want to use them (Like, okay, I can "sense the universal mind," now what). Only the Time sphere really seems to have a clear escalation of utility, but even then you're kind of limited if you want to do anything but break the campaign over your knee.
Overall, I'd say this book is pretty skippable. They had a chance to really go all-out and show what the top of the power curve looked like, but they decided to go another way with it. Not that the religious themes weren't interesting on their own, but 87 pages weren't nearly enough to do that subject justice either.
One last thing of note - this is the origin of the infamous Avatar Storm. Since my first Mage book was the revised core, I kind of thought that was just how it worked. "Of course you're going to get the shit kicked out of you if you cross over into the Spirit World, why do you think they call it 'The Guantlet'?" However, now that I see it in its original context, I can see why it was so controversial. The penalties aren't quite bad enough to justify the "you're not allowed to go the umbra" arguments I remember from back in the early aughts, but it does feel a lot like a mission statement. Personally, I'm inclined to keep it, even so, but I understand why people hate it.
Ukss Contribution: When talking about the various supernatural creatures that Archmages might be friends with, it mentions that the Corax, were-ravens, "have an amazing intelligence network." And while that was surely not meant in a completely literal way, I can't help but imagine suave, were-raven spies. It's like they have their tuxedos built-in! Cute.