There is huge potential for making the Reforms really hardcore, such as Rome only gaining mail armour after fighting against celts wearing mail etc. M2TW makes reforms very easy as new recruitment and buildings can be triggered by events, but this is a really simply, linear way of doing things. The romans went through the Marian reforms because they was fighting against too many enemies and was running out of man power, not because they suddenly decided one day to do things differently.

Thankfully M2TW also let you simulate the decline of the successor states military power, by reducing the amount of elite cavalry (and other units they rejected) available to them as time passes etc.