The Boredom of Large Empires...

[QuintusSertorius]

I've found playing in M/M and roleplaying to give the best experience, along with using Force Diplomacy to put the AI back in its box when it goes off on one. If you expand slowly (and I mean at the rate of about one province every 3-5 years) and give the AI time to adjust to the way things are, it doesn't tend to be as bad. What is also fun in the later game is punitive expeditions and trying to maintain a balance of impotence amongst the AI. Without treaties or anything, intervening on behalf of weaker factions and reducing the capabilities of the stronger ones. But never conquering anyone, just making sure no one gets too powerful.

But to prevent the game going boring, I spend more time managing the AI than my own faction (and another reason to expand slowly and not take too much territory is to avoid turning the game into primarily settlement-management). I do my faction things, then turn off the fog of war and look for who needs money, which armies need moving, and occasionally who needs to be made to besiege something. I also give shed-loads of money to the rebels at the start and boost their garrisons; they're a really effective bulwark against too-rapid AI expansion in the early game.