A question of reciprocal behavior... It was mentioned before that if the player used spying as much as the AI does, they'd be perpetually hated by all the AI's. Does the AI use spying against other AI's? If so, do they respond diplomatically the same way if they get caught? The answers to those questions could speak to a serious difference between the way the AI treats a player vs. another AI, with potentially frustrating results. I am reminded of earlier versions of Civ, where the other Civ's had zero tolerance against trespassing, but the AI would constantly trespass against the human player. You either had to let it happen or declare war, and the AI trespassed too often to maintain peaceful relations. It limited the play styles that were available. That's why I like how in Civ4 you have to decare war to trespass with an army.