[araes]

I would extend that to say that Diplomacy is still probably one of the weakest features of Civ.

It has been a joke since the original that dealing with the computer is like trying to barter with a schizophrenic, and sadly newer versions have only gotten a little better. AI's will still go from "I love you and want research agreements and luxury trades" to "I denounce you" and verge on war in the space of a turn.

Notably, the addition of the City-States was a big improvement, as they mostly respond logically, and their trend over time is to stabilize back to zero. They also provide you clearer guides on their emotional state and what actions will +/- it. If the main AI players were closer in the information they provided, and the options you had for interacting with them (ie, you could do things like destroy barbarians near them or gift them back their workers to increase your friendship) then the main AI might actually be reasonable to play with diplomatically.