So the change that I'm most happiest and also the most frustrated with is the combat.
how stacks are gone and how ranged units are actually ranged. It's feels really tactical now to actually arrange your units into a real army with flanking and terrain really coming in to play. On the other hand, manuvering your units into place can be an exercise in frustration, especially in hilly terrain where most units can only move 1 tile per turn. In a game I was playing today, I was trying to defend a city state from the evil forces of France, but the city state was right next to another neutral city state which had its own units roaming around the area. It became a horrible nightmare to get anything where I wanted it because the neutral city state kept inadvertently running interference and everything just became gridlocked. I imagine that after some more practice it won't be nearly as annoying, but it'll take some getting used to.