After purchasing the pdf of this to pull the economic system from it for my D&D game, I was very impressed by the entire book and decided to make it my go-to fantasy RPG system.
If B/X D&D had stayed the gold standard for Dungeon and Dragons rules instead of dying off in the wake of AD&D, something like Adventurer, Conqueror, King is likely what it would have morphed into (at least after people realized that they were never going to stick with a BECMI game long enough to reach level 30 and wanted something a little more feasible).
First of all, it is the best presentation of race as class that I have seen in an OSR product. Instead of allowing players to just be "a dwarf" or "an elf" as their class, each race gets a few racial classes that they can pick from, giving players who want to play demi humans a little more flexibility in their choices.
It also has a large focus on the "conqueror" and "king" aspects of the game. Rather than just saying "you can build a stronghold and attract followers at level 9", ACKS gives you solid rules about how you would go about doing that. Rather than just a cool side thing that you can do, this game fully expects you to embrace that style of play at high levels.
All of this, of course, is placed on top of a dead simple B/X-like ruleset that is easy to learn and gets out of the way when playing.
I like this interpretation of the Basic D&D rules system and the tweaks they made. I subtracted one star for typos because I'm a tech writer and I have high standards. The rules themselves are fine and very workable and flexible, allowing the GM to present a fun game and the players to have fun exploring the setting.
Very impressed with the book. Love the domain rules and tables for buying things. Saying that I have never been a fan of Demi human races as classes. Anyway enjoyable and useable even if for other games.
My favourite OSR system, by a fair margin. The racial class systems and proficiencies are each a good compromise between old and new, and the domain management and mass combat rules are great to pick out of it even when I play other things.
The best OSR system I have yet come across. While I have no immediate plans to run it, this doesn't matter because the it is filled with stuff that other fantasy RPGS critically lack and can be harvested and plugged into anything that fits the template like something I currently already have going on. This is mostly about acquiring, maintaining, and expanding a keep/home base as well as masses of NPC followers.