From the Official website blurb:
Kohan: Ahriman's Gift is the stand-alone prequel to Immortal Sovereigns. Experience the world of Khaldun from a whole new perspective: evil. Lead armies of Shadowbeasts and Undead as you ravage the countryside, driving all enemies before you.
Ahriman's Gift not only provides new campaigns and improved artificial intelligence, but also introduces dozens of new heroes and units to control.
Two new political factions and two new independent races.
5 campaigns to explore and conquer and an additional 40 custom designed maps.
Robust multiplayer support for up to 8 players.
Random map generator and map editors to custom make your own Deathmatch, Scenario, and Campaign maps.
Over 90 beautifully detailed units and over 70 different heroes.
Over 100 spells and over 75 technologies that will enhance your strategy.
30 different AI players challenge you with various styles of play.
Seven different game types (including Bloodbath and King of the Hill).