While there is a thread on the official forum for this, it has morphed into an interesting poison thread and I don't want to be the one to wrangle it back. So I am inquiring as to what house rules you use in your game. Mine are as follows:
Ogres are a race separate from Mountain Apes and much smarter (Int would go to 12 if a player race). They wear armor, use weapons proficiently and are not all about combat. There are very few Ogre Magi who are their leaders and protectors. Dwarves...as I am running a mostly RAW campaign the players are all by the book human types. So I took dwarves further and made them chaos dwarves, much fiercer than those in the core book and aligned with the minotaurs secretly. There are two strains of these dwarves, the bat-winged dwarves and the more Warhammer kind. Both types are mean and not to be trifled with. I added two gods, one a Nurgle-esque plague god and another a combination of Nyarlathotep and Malal (old Warhammer renegade Chaos god). both are just getting their claws into the setting. Goat-headed beastmen bring the renegade Chaos god with them. I add spells, items and monsters from my blog randomly. Exploding dice. Roll a 1 to Hit? Let's see how bad that can be.
Otherwise it is rules-as-written. With the group I have being new to the setting for the most part running the basic rules as is and then adding a little flavor and spice to make a different flavor of stew is very easy.
I haven't started a campaign yet, but I was thinking of keeping it simple. I'll likely run Hyperborea as-is, but use Holmes' Bluebook for the rules. Once (and if) the players get into the game and setting, I'll slowly add rules/options from AS&SH until we're playing it full-on. I'll still probably stick with simplified Holmes-style combat, though.
The other thought that I had was to just use all of the AS&SH material as a basis for an OD&D game. I even thought of making my own unofficial "Supplement" book with a basic gazetteer and necessary "house rules" - yet another project.
I wish I could translate the setting to Mythras for rules, but I don't know that I can do the classes justice, not as outright classes, but as packages. I might try in my home game, but I run AS&SH in a bar and the rules are pretty smooth for this.