Things I liked most about MoM was Adamantium Halfling Slingers. Cast Eldritch Weapon and Flame Blade on 6-8 of these units and you could slaughter almost anything in the game. Add a hero with a maxed out Leadership ability and these units were unstoppable.

I also like the Transmute spell along with the Raise Volcano/Change terrain combo spells to terraform the land around my cities to get the most out of where my city was located. The bonus was that a Volcano converted to a Mountain sometimes pulled Mithril, Adamantium, or other minerals from the ground which could be used by my city.

The last thing I like about MoM was the advantage of the Flight spell. If I attacked something that couldn't fly, I could try to use my flying unit to attack or successfully "done out" the 50 turns to escape unharmed which also assisted in scouting lairs and such.