In some respects, Armory is Starfinder's version of Pathfinder's Ultimate Equipment: a book filled to the brim with weapons, armors, adventuring gear, and magical items. However, unlike Ultimate Equipment, Armory isn't a compilation of equipment that has appeared in other books--it's mostly all new material and also includes some new class options. It's the sort of book that certain types of gamers will absolutely love (spending hours poring over the detailed entries for how to best outfit their PC) and others will find a relatively boring reference book to be pulled out occasionally. I should also note at the beginning that it's only 159 pages, continuing the Starfinder trend of comparatively short but expensive books compared to the first edition of Pathfinder.
The book starts with a two-page overview that's essentially a series of very general, sentence-long descriptions of each section of the book. It can be safely skipped without missing out on anything.
Formally, the entire book contains only two chapters: "Equipment" and "Class Options". But each of these chapters is broken down into several sections--the "Equipment" chapter, for example, has fifteen sections and is 137 pages long. A book like this isn't exactly a joy to read cover to cover--much of it is table after table of gear, with occasional two-page spreads of artwork and brief descriptions. I have to give credit to the writers of the equipment descriptions--I don't know how often people actually read the fluff (compared to just evaluating stats), but some of it is pretty interesting! As an aside, I find Starfinder's economy hilarious at times--you can buy something like seven armed helicopters for the price of one set of spiked knuckles that do 6d10 damage. Anyway, here are some very brief comments on each section.
CHAPTER 1: EQUIPMENT
* WEAPONS: The section introduces dozens of new weapon special properties, such as "free hands", "guided", and "subtle". There are also some new critical hit effects, including some really powerful ones like "suffocate." I'm glad the disintegrator line of weapons from Dead Suns made it in. The section also includes some basic "legacy" type weapons like greataxes, lances, and mauls. I've never taken the time to use them, but there are some new special manufacturer modifications that can be added in to any weapon. In sum, there's something like 50 pages just on new weapons, which gives you a sense of how much gear is crammed into the book.
* WEAPON ACCESSORIES: These are things like scopes, collapsing stocks, flash suppressors, etc. I don't like how bayonet brackets make every pistol-wielding character able to take AoOs, and I've also encountered problems in games due to bipods and scopes/sights serving as very cheap and easy ways to negate cover.
* WEAPON FUSIONS: There a lot of clever, useful ones here. I particularly like "advancing", "conserving" (a life-saver for one of my PCs), and "guarded".
* SPECIAL MATERIALS: These provide pretty minor changes--I probably wouldn't bother.
* ARMOR: I like the description and artwork in this section. There are a lot fewer types of new armor then new weapons, but there's also a lot fewer variables to work with. I've used the new "mining jack" on a dwarf PC and "regimental dress" on a Steward PC. As an aside, I've never really noticed before that around level 8 or so, the difference between light and heavy armors of the same price isn't very significant.
* POWERED ARMOR: This section has a special new rule that makes all powered armors upgradeable to any level (if you have the credits to pay for the alterations). It also introduces several new suits of powered armor, and there are some cool concepts here, though I've never tried any of them.
* ARMOR UPGRADES: There's over 70 new armor upgrades here, and although there are definitely some "meh" ones, there's bound to be some good ones too. I particularly like the auto-CPR unit, the auto-injector, and the computer interface ones.
* AUGMENTATIONS: Be the Bionic (Wo)Man! Some good choices here, including regenerative blood and synchronous heart. My favourite might be the optical laser just because I love the image (even though it doesn't really do much damage).
* TECHNOLOGICAL ITEMS: A ton of stuff here, and something for everyone. Dermal staplers, grenade scramblers (!), and a lot of useful drones. Tool kits are overpowered, giving really big bonuses to some skills for a very cheap price. It's also weird that every single thing you can buy here gives some sort of mechanical bonus, even goofy things like board games.
* MAGIC ITEMS: There's a good selection of some classic and some new ones here. Consumables are still way over-priced for what they do. A couple of items, like the containment tesseract and the trafodi paradox, would make for good plot devices.
* HYBRID ITEMS: These are techno-magical items. The captive star amulet is useful, and I like the creator capsule. Mischievous folks will have lots of fun with wonder grenades.
* PERSONAL ITEMS: If you want to buy an umbrella, some perfume, or a sleeping bag, this is the place. Aerosol spray is a really cheap way to find invisible foes!
* DRUGS: My drug-addicted solarian would like to note that drugs are still way-overpriced for what they do. It costs 23,500 credits for just one dose of an excitant to gain immunity to sleep effects for four hours! That's more than it costs to own outright a Level 8 Armored Transport vehicle.
* OTHER PURCHASES: This catch-all section actually has some really important information. There are rules for buying medical treatment and for hiring NPCs to serve crew roles on starships (great for small gaming groups). I like the little capsule descriptions of the different cuisines of the Core Rulebook races.
* VEHICLES: I've never really done anything with vehicles in Starfinder, but if you have 3,750,000 credits to buy a Level 20 Ultimatum Hover Carrier, this would be the place.
CHAPTER 2: CLASS OPTIONS
This section is 16 pages long and contains two pages dedicated to each of the Core classes. A two-page intro contains a new archetype, "Augmented", which is a Verces-themed option for characters who are heavily into artificial personal upgrades. It's passable.
* ENVOY: They receive some new improvisations and expertise talents, and overall there are some good additions to the game.
* MECHANIC: Some new tricks; "Tech Tinkerer" adds a lot of versatility to a character. Many of the options also help with starship combat. For drone fans, there are four new mods.
* MYSTIC: There's a new mystic connection, "Geneturge", which is all about DNA. Two new spells support the connection. Kinda fun, and I like the idea of having a self-help guru Mystic.
* OPERATIVE: I'm firmly of the opinion that operatives should be stripped of options rather than getting more. Anyway, this section contains several new exploits, with Trap Spotter extraordinarily useful (providing an automatic chance to detect traps just by getting close to one). There's a new operative specialization, "Gadgeteer", that's fine (and fun when combined with the "utility belt" exploit).
* SOLARIAN: Several new stellar revelations and a couple of new zenith revelations. Solarians who use stellar armor get a couple of nice choices. I love the quantum entrapment zenith revelation--send a foe out of reality for a few rounds!
* SOLDIER: Several new gear boosts accompany a new fighting style called "Shock & Awe". It's kinda silly, but fun to imagine.
* TECHNOMANCER: Four new magic hacks and three new spells. The "enchanted fusion" magic hack could be useful in helping to exploit particular enemy vulnerabilities.
And that's the end of the book. To be honest, if I wasn't a collector/subscriber, I probably wouldn't buy this book--all of the gear and class options will appear on Archives of Nethys anyway, and there's no major campaign setting details or other flavour that can be found only in the PDF or physical copy. Starfinder Society players, however, will no doubt find it handy to have so many additional options.