Let us open this post about Magic in the Shadows (Stephen Kenson) with the ceremonial pointing out that fuck, man, Shadowrun rules expansions really love expanding the rules. Set your minds at ease - you will need to make a lot of dice rolls, some of which are for incredibly piddly shit (after your roll to gather wild alchemy materials, you will need to make a roll for refining those materials into "radicals" and then another roll to turn those radicals into magic items) - all is right in the world.
I suppose the rules feel a little less intrusive here than in Rigger 2 and I think that comes down to the fact that we're talking about magic. You've got a rule for everything because the rules legitimately define what you can do. There's no background reality that allows you to infer the existence of quickening spells or great form spirits, and thus each new rule gives you a genuinely new thing to do that you couldn't before. It feels less onerous. At no point are you in a situation where, say, you want to jam a radio signal with a civilian transmitter that has been illegally boosted in violation of FCC regulations and the GM is like, "sorry, but there's nothing in the electronic countermeasures rules about this." When you're asking, "hey, can I use the macguffin to make unobtanium?" then "no, you can only do what the description says you can do" is a perfectly valid response.
Which isn't to say that there's no room for hard feelings and contentious rules arguments. They just mostly come in the form of power interactions. Like, can the new Adept power "Delay Damage (Silent)" which allows you to gently touch a target and then, up to 24 hours later, have them take full melee damage, as if you'd hit them full force, combine with "Distance Strike" power, which allows you to make melee attacks at range, so that you can just harmlessly gesture at someone and have them drop dead of no apparent cause?
I'd be inclined to allow it, because it's a really specialized build, basically requiring all of your starting power points to get off the ground, but I'd be a little nervous about it. Normally, I scoff at charging PCs for "natural weapons" because real weapons are trivial to acquire in all but a few very specific scenarios, but a perfectly concealable, perfectly inalienable gun does become something a bit more than "yeah, okay, you're armed in prison/the fancy dinner party/bank lobby, but so are the guards" when you can also use it undetectably and then act really shocked when your target drops dead.
On the other hand, we're talking about heist capers here. You can spec to be the perfect assassin all you want, but when the fight is against militarized corporate security because your overly-specialized ass accidentally tripped an alarm, you're probably going to want some more overt firepower.
The more interesting question is what implications these powers have for the setting? If there are people who can wave at you and make your head explode, how does this change things like the public appearances of politicians and celebrities? What is this doing culturally?
There is some talk about these issues, unfortunately it's pretty brief. We learn that mages who commit crimes are basically tortured, because the only way to stop them from using their powers is to blind them, immobilize them, and drug them. Oof. Also, healing magic is treated with skepticism by the medical community, and the main commercial applications of sorcery are extremely specialized high-tech research and trivial stuff in the entertainment industry, with absolutely nothing in between.
I'm a little disappointed, but I suspect it's an intentional choice. Shadowrun is a blend of cyberpunk and fantasy, but the cyberpunk is the senior partner in that relationship. Magic is used as a kind of anti-cyberpunk - it is small scale, bespoke, fleeting, and incompatible with most technological or industrial processes. It's a thing for anarcho-primitives, traditional communities, hermits and renunciates, and other people who don't fully participate in modern capitalism. It's extremely useful for living by yourself out in the woods, but you can't package it for mass consumption. That's probably thematic.
Though I also suspect it's a theme that's partially driven by game balance. Almost all the magic we see in the books (with the exception of the ritual magic used by the Native American Nations to defeat the United States government) has been stuff that's been relatively safe to give to Player Characters. The limitations of magic - it's rarely permanent, it doesn't scale, it needs prodigious amounts of xp - are also the rules you'd put in place to prevent magician characters from breaking the game.
On the whole, it works. I like Shadowrun's world just fine. You can be an elf ninja, using your arts of invisibility to steal from a corporation and the corporation will maybe be a little frustrated that they can't monetize invisibility for themselves, but they'll also just respond by putting hellhounds and fluorescing astral bacteria (a type of magic that can be mass-produced, but doesn't do anything but hinder PCs, so it's okay) in your way. You're never going to worry about the philosophical or political implications of high-fantasy ideas like bringing back the dead or floating sky castles because things need to stay within a fairly narrow sci-fi aesthetic. And maybe I'm wired to be more curious about questions like "can you use detection magic to observe subatomic particles" or "can sorcery and/or conjuring build a house faster or cheaper than manual labor and modern machinery?" But what genre is that? Fermi-core? Post-Scarcity-Punk? The aesthetic is narrow because it's a good aesthetic.
In the end, the best and worst thing I can say about Magic in the Shadows is that it's a great supplement if you're interested in rules-heavy low fantasy that focuses on small unit mercenaries who commit elaborate heist capers for pay. That is its wheelhouse and so long as you stay in that box, it offers a lot of fun new content - different magical traditions like voodoo or wuxing; new types of spirits like blood elementals or ally spirits (like familiars, but a bit tougher . . . if you're willing to invest obscene amounts of xp); new totems for shamans, including crab, prairie dog, and goose (putting me in the awkward position of having to decide between condemning the egregious cultural appropriation and indulging my intense desire to play a magician who gets his powers from a magic goose). I think, overall, it's probably the second best kind of new Shadowrun content. . . just behind Important New Metaplot That Will Change Everything Forever.
Ukss Contribution: "The Mojave Desert is aspected against Conjuring, making any use of the Conjuring skill there more difficult - much to the satisfaction of the spirits there."
And I don't know why, but this is such a Shadowrun detail. Like, the whole game is thoroughly American, and it can be bad like America is bad, but it has this . . . yearning. It manifests in this particularly 90s form of romanticism where somehow the goodness and the holiness that has been systematically pushed out of our capitalist economy will manifest in the land. You go out into the Mojave and experience the starkness of its wide horizons and you think "here live the gods we have abandoned for our greed."
I could make fun of them, because this is sort of thing that seems like it was included because it feels vaguely Native American, but if I'm being honest, it's something I've experienced personally.