you can now choose to develop settlements into castles or cities. The former are hard to conquer and allow you to produce tough miltary units early on, the latter can grow really big and return huge trade profits. And have diplomatic strengths, etc.

Another thing is that cities and castles will no longer have a generic build structure but will 'blend in' with the environment and the buildings it holds. So a city in a mountain range or near a stream will have added defense perks, one can assume.

There will also be princesses that can wed with one of the other factions' heirs to strengthen your alliance's ties, and a general increased focus on diplomacy.

In that regard: much like the senate in RTW, you will now have to deal with the Pope as an external regulating entity. He will, like the senate, issue certain assignements (do a crusade on the Turks etc), or send inquisitors to your land(s) if they aren't zealous enough. They'll kill highly placed officials. Surprised If you really fuck up in keeping your lands pious, the Pope can excommunicate you, which basically means all the pope's buddies will try to pwn you.

But you can also use him to your advantage: there's the obvious bonus of money and standing of being on a good slate, but you can also coordinate attacks on excommunicated states if you you're a good buddy of his. Twisted Evil Or, even better, you can lobby one of your cardinals into the papacy, should the old man die. Sweet!