I second this all:

Quote Originally Posted by Claudius the God
the ability to create moats...

I want news of glorious battles from distant lands... If my ally or enemy has suffered a severe loss, then I want to know about it...

coastal provinces should be able to build a fishing industry in addition to naval industry and naval trade...
Quote Originally Posted by Ironside
Reappearing factions has to come back.
Quote Originally Posted by Baeksen
Improvement of the campaign AI so that it will be capable of composing an army in a reasonable way. Meaning that you would have to fight armies composed of a range of different unit types that complement each other and no longer fight armies completely missing a type of units, like ranged units.

A town guard that can be summoned to protect a city under siege, but not leave the city. This would make siege battles more exciting, as you would be able to man the walls properly. This town guard size and quality could be dependent on factors such as city size, buildings in the city, culture and loyalty towards the faction leader and the local feudal lord.
Quote Originally Posted by boastj
The ability to move several stacks at the same time on the campaign map by clicking and dragging (I was just playing as the Huns in BI and it was getting annoying moving them individually)
Quote Originally Posted by Weebeast
I'd love to continue playing even if my king dies without a heir. Just because a line dies doesn't mean everything becomes non-existing. Let one hi-rank general lead the population to carry on as if it was a civil war and let me play it.
Quote Originally Posted by Spino
Instantaneous movement of all diplomats, priests, princesses, spies & assassins from one unblockaded port to the other. I think it's silly that these units should be dependent on military fleets for transportation as they are in RTW. During times of war simply factor in the chance that these units can be intercepted and/or eliminated by an enemy fleet within a certain distance of either port whenever they attempt to travel overseas.
Quote Originally Posted by hrvojej
This could be done with the ability to see the stance of other factions towards your own, and with the AI that will act in accordance to those stances. If you have friendly relations with a faction, you should be able to have some feedback about that (the more detailed the better IMHO), and then you would know that they are less likely to backstab you etc. This doesn't mean that friendships should be easy or cheap to gain, but it should add a whole new dimension to the campmap strategy and gameplay. This should make diplomacy much less of a haphazard guessing game that it was in the previous TW games, which basically meant that I would just not bother to use it at all.