Just backing up some of the other comments here about the difference in "style" between Western and Eastern armies. If you get good at the tactics involved in running a cavalry-based army with mobile archers (something I'm still trying to improve), and can handle the additional micro-management on the battlefield, then Eastern armies can be devastating.

This is a case where hands-on control trumps stats; mobility allowing your HA's to fire from all sides to defeat frontal armor like shields. But it is some extra work during a battle, and sometimes I prefer Western armies for the way you can basically determine the battle's outcome with a good initial formation, enough men to balance your opponent, and a little use of cav on the side. There are in-between types of armies too, like the ones you get playing the Hungarians; a Catholic faction with its major strength in cav and horse archers.

This ability to play several different ways on the battlefield is one of the games major strengths.

P.S. RTW is a good game, especially the modded versions. M2TW does have slightly better tactical AI, and the campaign is a little deeper with the added elements like princesses, merchants, crusades, jihads, etc.