Concentrating on the late medieval period, Age of Chivalry: Hegemony replaces or significantly alters each of the civilizations in the original game, while adding a number of new ones, allowing the player to control Central and Western European states. Many new units and technologies have been added and gameplay dynamics have been changed considerably in this complete overhaul of Age of Empires II.
This game has units that are so well researched, I have to speak Italian to use Goggle and look them up.
Also it's really well done, very pretty.