Inside the Old World Armoury you will find a definitive guide to coinage, a detailed look at armour with new armour types, heraldry guidelines and variations by nation, an enormous selection of equipment, new poisons, draughts, and oddities, rules for animals and transportation, guidelines for owning property, rules for hiring characters, and a selection of treasures.
It's useful, but the way the book is written makes it a slog to go through. There are sections which literally explain to the reader what a Cow and a Pig are. Others give twice as much space to describing a simple thing than is needed. Others still repeat information literally paragraph after paragraph.
It's basically a toolbox for making your Warhammer game more detailed and mechanics-rich, and personally I'm all for the former, but feel entirely uninterested in the latter. If you're like me, this book is little more than a list of weaponry and items that you might not normally include in your game, but will likely want to after reading it. But how it's supposed to actually work in-game, is kind of questionable, and hence my remarks about this being an opt-in toolbox more than anything else, not an opt-out lore expansion like many of these tend to be.
3.5 stars. How much use someone gets out of this depends entirely on the person. It is bursting with stuff to put into a Warhammer Fantasy campaign. Weapons, armor, vehicles, clothes, foreign coins and exchange rates, animals, hirelings, and on and on. With each of these new cool things, though, comes more mechanics, more dice rolls, more things to keep track of, and more crunch. No one in their right mind would use absolutely everything in here all at once.
The best way to use this is to just pick up a thing or two that seems interesting or fun, or maybe something specific to a particular campaign (vehicle combat, foreign weapons and money, etc.). I do think that there is probably something in here for everyone, though.