The campagn is adjusted to be played in 12 turns per year and with the highest movement ranges to simulate congruent time-range movement for armies. Also campaign is much more slow peaced so don't think about conquer the whole map in 4 years.

Buildings:
Now buildings are around x3 times more expensive. They can take between 6 months to 4 years to construct. I'm thinking about to increase to even more realistic (so even more turns) times some of them, like monuments or city developements. Vanilla population and building system is very simplistic and doesn't makes you think on resources or developement strategies, you just build the next building. Now the resource investment needs to be much more planed.

Population and hapiness:
Now workforce (yes we can use it as an actual pop sistem) have a big impact in resource production, recruitment slots, construction, hapiness, replenishment... Now growth is much slower so in some provinces you really will need to estimulate growth, migration or satisfaction if you don't want to be stuck with a poor unproductive province. Recruitment delete 1 pop slot per unit. If you disband a unit you get 1 aditional population slot in a ramdom province.

Edicts:
As mentioned before the pop system have a big impact in economy and recruitment. Recruitment edict can save your ass to face an invasion if you are on a delicate situation inproving recruitment max slots and boosting replenishment. Check pros and cons of every edict.

Recruitment and manteinance:
Now professional units like guards or chariots need time to properly train their men. So some units are going to need 2, 3 or 4 turns to be kicked out of the barracks and start their duty. Armies in foreing or low influence territories are much more expensive to mantain due costs and longer logistic lines. Fill your forts, improve your garrisons and save resources to prepare your military campaigns. Replenishment is much more slower and linked to men abaliability. You need to be encamped or in a settlement most of times to replenish.

Diplomacy:
Take time and resources to improve your diplomatic relations. Make marriages, try to get allies and other deals. Conflicts and wars are going to appear aniway and the game is going to penalty you a lot if you just try to be the aggresive conqueror without taking care of the help or resources you need. Imagine be at war with a neighbour and then suddenly 2 other factions declare war on you, just because you didn't chek diplomacy regularly...

Disasters:
Now they have bigger penalties and your provinces really feeling like being on serious trouble and not just "-10% income". Be prepare to face drastic changes in your provinces. You really need to take care of management, building, diplomacy and savings to progress in campaign.