[Taqwus]

Among the more significant differences wrt MoM, I'd say, are --

Designed for heavy multiplayer from the get-go. Means -- many very different sides possible; no direct control in combat (doesn't scale); you organize troops and script orders during your turn. Interleaved strategic order execution rather than IGO/UGO.

More of a serious mega-wargame flavor than a heros-vs-monsters game, with sieges, supply, morale checks, fatigue. Detailed stats and rules, ex. shields provide benefit IF a parry works, long weapons can repel those using shorter ones, et al. Also, more commanders running around -- you NEED them for troops to move between provinces -- less emphasis on crafting mega-items for a few incredibly powerful heroes as you'll need to split magic resources for a few uses.

Dominion concept. Belief spreads. No believers, no nation. You might have the most provinces but be doing badly in dominion if you neglect dominion strength, temples, priest... or if you're Early/Late Mictlan and don't sacrifice enough humans.

More stealth. Stealth, patrols to detect stealth, spys which can cause unrest in enemy provinces, assassins to take out enemy commanders, whole stealth armies led by stealthy commanders attempting to sneak through a warzone to raid deep in enemy territory.

Map design: provinces versus squares. Provinces can hold a -lot- of stuff -- no 9 hero/stack limits here. Provinces have population. Provinces provide local troop types.

No real city development. Buildings are fortress (assorted types), temple, lab.

More complex magic system. More commanders can cast. Items and spells can require two paths of magic, not just one. There's both fatigue AND gem cost, if you're tossing spells in battle. Research is level/area, not individual spell, and spells can be restricted to different nations. Gems need to be used for both spells and items, so resource management matters.

Very, very moddable. Create a new nation if you like. Remake an existing one. Make all spells available at the start. Eliminate "Dispel" (!). Make the 'Luck/Misfortune' scale have far greater effect on random event likelihood. Create multiple identical nations for a bizarre tournament. Create a terrifying flying, mindless, headless monster with 1000 eyes, four life-draining tentacles, immunity to fire and even radiating heat, but with vulnerability to shock and no aptitude for magic, and offer it as a pretender type to a few nations.