“I think its safe to say that I have never seen a set of rules and guidelines for stronghold and dominion management in any other D&D game (or even any other game remotely similar to D&D) that were this complete. The mechanics in the BECMI/Rules Cyclopedia books pale in comparison. Even Pendragon, which probably has the most detailed rules on manors that I’d seen systematized until now, doesn’t really match up. You get complete rules for just what kind of stronghold each class can make, how many followers it will attract, what every little bit of it will cost, how many peasant families you can attract and support, and what kind of revenue you can collect. On top of that you get rules for how to expand your domain, what kind of various expenses are involved on a regular basis, rules and tables for being a vassal of a lord or king, morale rules for your dominion to see if the peasants are revolting, rules for building and running villages, towns and cities, and building and managing markets.”
These are the ones that always jump to mind for me:
Campaign roles for the classes
Dominion Rules
Stronghold Creation
Trade and Arbitrage
Balanced Economics
Magic Item Creation
Two more:
1. Throws and rolls. It makes it so much simpler than any other system to explain what's going on to new gamers or my friends who never give shit and just want to kick ass.
2. The class system/proficiencies. Easy to customize, without adding a skill system that's so annoying in 3E. You can be a berserker and don't have to spend 32 points on silly skills like Search or Observation or whatever.
I don't know how to word these well, but they're features that led me to ACKS as my favorite system.
You probably also want to just list basic stuff like what races and classes are included. I know that's always one of my first questions when looking at a D&D type game.
Some aspects of ACKS I am quite proud of:
Throws and rolls
Proficiency system
Permanent wounds and weird side effects from mortal blows
Improved combat effectiveness of fighters
Improved thief mechanics
Unique dragons with special powers
Cross-breeding, necromancy, divine power
Hijinks
Balanced economics
Magic item creation
Hijinks are very awesome, it's worth some brain cells figuring out how to describe the mechanic in a bullet.
You might want to mention the presence of classic character classes along with more unusual, campaign-specific ones, like the Bladedancer or Craftpriest.