Have you ever had a battle where everybody on both sides dies except for the two kings, and they both duel each other to the death? Isn't that great?
I remember one particular battle where all of the Byzantines and all of the Turks were slaughtered except for my Sultan and Emperor Alexius III. They both charged at each other and fought amidst the thousands of dead bodies strewn across the field and in the pouring rain. For several minutes they fought each other, until finally the Sultan slew the Emperor and I conquered Constantinople.
I also remember another battle where I captured both Alexius III and Commenus...that was great, too.
I have really only played two games of Medieval Total War in all the time I've owned it (been occupied with life and other games), so this may be common to everybody, but the first time it happened to me it was really spectacular.