For me personally the civ switching is the big one that makes me not want to play the game.
the game actually has many great mechanics like diplomacy, combat, graphic details, rivers..
I would like a mode where I could start in ancient era with any civ like Russia or France, and also ai empires would be randomized so the opponents would not be only ancient empires like Aksum.
I miss the discovery of who the neighbors.are.
Then there would be no switching, the civs would stay the same till the end. I dont mind that there would be no unique units for each era.
So I consider myself a potential returner to the game.