This is probably one of the most lengthy and in depth works in the OSR, and definitely belongs right next to the Rules Cyclopedia in terms of indexes of rules.

The clever usage of subclasses means that the game can have a wide range of parties while sticking to the traditional four classes of classic D&D.

Simplify, and then show depth seems to be the motto here. You start with fairly traditional retroclone rulesets, before giving rules for stuff such as dual wielding and phalanxes. The exhaustive effort put into this just shows.

All in all, a really good product for if you're in the mood for playing some classic swords & sorcery rpg gaming.