It's funny that, looking back at my original post about ACKS, I was interested in it as an alternative / "for comparison with" Fields of Blood, but I never got around to writing such a comparison.
Fields of Blood is an old 3.x supplement that basically did the Domain Game. Looking back, it did some things well and some things poorly, and there are definitely lessons to be learned and good ideas to be stolen from it.
A systematic review:
The introduction is unusually long at three pages, providing a glossary, a simple example of the core combat mechanics, and a brief rundown of the contents of the following chapters. I think this is clever; you may not fully grok the meaning of each term without context, but skimming them here "loads" them for later comprehension and memory.
Realms are discussed next. Realms have a species, a sort of "tech level" ranging from Nomadic to Civilized, and a government style. These aren't particularly well-considered or historically justified; they're at a similar level of accuracy to civilization and government traits in the Civ games (which is to say "minimal / inspired by"). Nomads in particular are beautifully overpowered, and the government types are really amusing to read, but they're sort of fun to play around with. Next up is terrain; hexes are 12 miles across and each is classified into one of eight terrain types. Mixed-terrain provinces are permitted, but basically just give the owner their choice of which to use. The production of each province is determined by the race occupying it and the size of the province's settlement; no distinction is made between rural and urban incomes, with the settlement size taken to be representative of the whole population of the area. While the economics of the game are frankly rather broken, going beyond 3.x's usual lack of concern and out into the realms of "buggy in play" / potential exploits, I think this merger of domain and settlement is an abstraction worth stealing for ease of use, as well as elimination of tracking population down on the level of individual families.
There is a list of improvements you can build in your settlements, including temples, thieves' guilds, wizards' guilds, economic improvements like irrigation systems and marketplaces, and of course fortifications. The presentation of the fortifications is notably superior to ACKS', in that it includes cost and combat statistics both on one table. They also use the same toughness/wounds damage abstraction for structures as they do for units, whereas ACKS has distinct structural hit points. More generally, I believe that these sort of upgrade-structures would do well in ACKS. ACKS' economic model is consistent enough that we can do the math and figure out how much it would cost to assemble and retain an Alchemist's Guild to produce Greek fire at scale, for example. It's just a matter of taking the economic numbers and turning them into easier-to-use quantized "upgrades" that alter the availability of goods in the market so you don't have to figure out how much it costs to commission a hundred kilolitres of military oil every time you need to burn a city to the ground.
Chapter the third covers the process of realm play. Realm actions happen on the scale of seasons, while military actions happen on the scale of weeks. Taxes, upkeep, and random events occur per season, with season-specific event tables. You get two regent actions and two realm actions per season (presented in 3.x's standard vs free action nomenclature). Regent actions are diplomatic or heroic things like annexing land, casting ritual magic, declaring war or peace, ordering espionage operations, and training troops. Realm actions are mostly building and upgrading settlements, improvements, roads, and so forth. Martial actions (orders to units) are then issued on a weekly basis throughout the season. I think making growth paperwork and income a per-season event is not a bad idea; it encourages the pace of play to slow down a bit and makes the work somewhat less onerous.
Their espionage rules may provide some inspiration for fixes to hijinks. The available espionage operations are spying (reveals information about an enemy province), infiltrating an enemy guild (temporarily reduce an enemy guild's level), and disrupting trade (temporarily reduce's an enemy province's income). Each operation requires two d20 rolls; one determines the effectiveness of the action, while the other determines that the ruler of the target province learns about the operation (unaware, aware but isn't sure who did it, and knows instigator). Thieves' guilds cost money to maintain, and can offer bonuses to defense against espionage as well as bonuses to performing espionage operations. This is more what I would like to see in hijinks; there's a chance to be unmasked while still succeeding at the operation, and they achieve utilitarian effects-in-the-world instead of just being magical economy-breaking goldfountains.
One thing that bugs me about both of ACKS and FoB is that domain growth is very much a function of the ruler's actions / reinvestment. I'm not sure this makes sense; I suspect most growth historically has been a result of benign neglect rather than active management. Lay off the taxes, leave enough surplus for the common folk to have and feed some extra kids and 20 years down the line they'll be working more land and producing more for your heir. Would be interesting to make growth a per-season or per year percentile roll to see if the domain's settlement has upgraded itself to the next size category, with accompanying increase in rural population and income, rather than primarily a function of dumping gold into the economy.
Chapter four covers unit construction. In classic 3.x style, it's complicated, with unit subtypes and feats and careful weapon selection for all your mans. Domains at War wins for simplicity here. The Shock Modifier is an interesting mechanic, in that it models units which are scary but maybe don't do all that much damage; one might expect the common spearman to be somewhat disheartened by fighting the undead, even if he's giving as good as he's getting. Mostly unit stats are based around 3.x's combat mechanics; AC and to-hit are unchanged, while damage is rolled into Power, Toughness, and Wounds. After you hit, you roll power against their toughness and if that hits too, they take a wound. Morale and command modifiers are present, but they're mostly small and rolled on a d20, so the dice dominate.
Chapter five is the mass combat rules. Nothing horribly insightful to steal from here. No command-and-control rules, morale is an all-or-nothing save-vs-flee-at-top-speed. Units get to-hit and power bonuses from having a PC leader attached in addition to morale and command. Their terrain rules are handled in paragraphs rather than as a trio of booleans, and there's a whole list of 3.x-style conditions for units. The siege rules are reasonablish. There's also a quick combat section closer to DaW: Campaigns' battle rules.
Chapter six is magics. Couple of feats, some conversion rules for personal-scale spells to battle scale, costs for realm-ritual magic. Regular units who come under magic fire only have to check morale if they fail save, elite units never have to for magic.
Chapter seven is heroes. Noble Birth is a feat. Some of the other feats are vaguely entertaining as well. The prestige classes are, well... prestige classes. Rogues sort of get the short end of the stick with these. Living Legion is hilarious (the premise being that you're one guy who specializes in fighting 100 guys at a time). A couple of the leadery prestige classes (Dreadlord, Hordemaster) might have things worth stealing
Chapter eight is on actually running the game. Includes guidelines for turning your map into a hex map, assigning government types, starting standing armies (40% of realm income by default; ACKS is closer to 25% by default). *shrug*
Appendices: converted spells to battle scale (Man I haven't seen Evard's Black Tentacles in ages! That was a hilarious spell; I used it once and then never again), new battle-scale spells, realm spells, most of the Monster Manual monsters converted to battle scale. Some of the realm and battle-scale spells would make decent rituals in ACKS; encircling an entire domain with a ring of fire or a bubble-shield for a full season is pretty rad.
Other things: the art is black and white and generally pretty good; I'm fond of it. There are some short fiction blurs at the beginnings of the chapters; about a half-page each. They tell an ongoing story of a ruler who inherited a domain and could've done a better job running it. I've read worse. The editing of the whole book is alright, though not amazing.
In conclusion! The economics are completely made-up, the unit creation is overcomplicated, and in general there's a lot of 3.x philosophy showing through. Realm/regent actions are a clear compromise between playability and realism. But their level of granularity is very gameable. Population is expressed as a ten-item enumeration of settlement types rather than as an integral number of families residing on the land, income from domains is in units of 100gp rather than individual GP, military units are hired as a whole rather than being constituted piecemeal from mercenaries hired individually, and realm paperwork happens once a season rather than once a month. These are things maybe worth stealing for ACKS.