This book... it is... *chef kiss*!
From an RPG standpoint:
This is the only version of a fantasy D20 that interests me. I'm not a fan of hitdice, armor class, spells-per-day or levelling mechanics, but this game has got me excited to try them again. It takes lessons and mechanics that Crawford has learned across his previous works (e.g. Godbound, Stars Without Number) and incorportated them into something flexible and meaty without getting bogged down in complexity. While it may look at first that there are only 4 classes (which I call "skill-monkey", "casty", "stabby" and "undecided") the use of skills, foci and arts are what really let you make a character so much more interesting and different than appears at first glance.
Foci and arts give you lots of ways to change your character up, and really change the rules and abilities for them. Want to make an agile fighter that dances across the battlefield and avoids every attack on their path? The "Close Combatant" foci has you covered. Want your little animal companion - a pet hamster - to become the most feared beast in the world? Take the "Shared Vitality" art as a beastmaster and watch little Hammy take on wolves as you level up. Want to learn how to toss bad guys into walls like a pro? The Vowed class's "Hurling Throw" art will teach you how to toss COWS!!!!
These change up the abilities of your characters so much it's a thing of beauty for me to read! And you get access to them readily and easily - so you can pretty much make any character you want!
And from a combat side? The rules are quite simple and surprisingly tight. Shock damage means that you and your enemies will very often be doing at least some harm to each other, which combines with the relatively low HP of everything to keep combats fast, fluid and wonderfully lethal. No one wants to be in a fight, and just because your armor can take a hit doesn't mean you don't still feel that warhammer smacking into you. Snap attacks give advanced warriors and desparate defenders a method to retaliate against their foes, and the requirement for a mage to not take damage so they can finish casting a spell results in "gank the mage" being a far more viable option than I initially expected.
From a GM/Toolbox Standpoint:
Okay, if the RPG part didn't convince you - either because you despise OSR games or something I said above just didn't click - then I would still recommend this book as a source for fantasy inspiration and worldbuilding. ~3/4 of this book is just for helping the GM create adversaries, create adventure seeds, populate the world with interesting and attention-grabbing locations, people, societies and conflicts. Factions can be statted out and their mechanics allow them to actively fight and compete over your world (with the PC's actions able to directly modify their capabilities).
And thanks to tools like the Azgaar fantasy map generator, you can generate a world in no time (just turn on a 6-mile hex grid and your players can start exploring!)
And the best part - it's system neutrual!!! While factions and creatures will definitely follow the OSR-style mechanics, the settings details are there for fluff and world building so you can import all of this to any other game or story you want.
As a final point, the OSR-style rules also make it easy to port other creatures, mechanics and ideas from OSR games with little effort - with Crawford's other games (e.g. Stars Without Number, Spears of the Dawn, Other Dust, etc.) being very easy to port over.
For the pricepoint of this deluxe PDF alone, I whole-heartedly recommend this book. The fact that there is a FREE version as well which contains everything I said above means that you can also try it out before you put your money down - which makes this one of the safest purchases and consumer experiences you can make!
Seriously, this is one of the best RPGs I own. This gets me excited to both play and run a game. This gets me stoked for fantasy worldbuilding in a way that nothing else nowadays does. And if this is what the heart of the OSR movement is, I can 100% see why it's coming back.
I think this game is absolutely amazing, and I want to encourage everyone who is on the fence to give this one a shot!
[5 of 5 Stars!]