Civ4 AI is very nice, especially since each leader behaves differently, and there is also an option for Random Personalties, which could lead to such madness as psychotic warmongerer Gandhi and peaceful builder Alexander. It is usually decently competent at war(and will actually pick on weaker AIs to good effect) and it is also capable of pursuing any victory in Beyond the Sword(people have actually witnessed AIs win domination victories.) They also pursue tech gambits(they are capable of, for example, setting up a Feudalism slingshot using the Oracle if conditions are favorable.) However, you won't find AI that is anything better than average when compared to humans.