I like the idea of the decline and fall as well. Parthians and the like were really meant for these later periods. I liked the way MTW restricted arbalesters/crossbows, and gunpowder to specific periods, then allowed us to campaign starting with an appropriate map for that period. I would like to see more of that with RTW.

It puts CA in a difficult position trying to create a game that starts very early, but contains units spanning about six centuries with considerable evolution of weapons and armies. Campaigns tend to last less than 100 years, so in order to keep it interesting a lot of compromises are made.