I think one thing that hasn't been discussed on the boards is combat. We all know Diplomacy was broken but I don't think any of us realized how beat up combat was until they decided to change it.
Things I have heard about combat rework:
-Each unit will now have 100HP as opposed to 10HP
-Artillery-like units will now be essential for taking cities that have defenses
-Artillery-like and ranged units will be treated differently (i.e. artillery-like will now have an inherent bonus against cities)
I think obviously 100HP changes combat entirely and allows for militarys to be smaller overall. Warfare will be less about sheer numbers and more about the terrain, tactics, strategies and type of units deployed on the battlefield. Obviously having a giant military is not a problem though.
To me flanking, pillaging and great generals (and all other bonuses) all become extremely relevant under this new 100HP system.