Surprised to see the opinions on V/VI not being as good. I've played every interation of this game and they all brought something to the table. VI and the districting gameplay added a lot to the game. One unit per tile in V also made combat more tactical than doom stacking around.
The big thing I'd like in a new one is less cheaty AI. It's just so boring that winning on Deity is basically exploiting AI foibles instead of... you know, building a stronger nation on an even keel. At the highest difficulty AI should get no bonuses but still be really good at playing the game.