As shocking as it sounds, I actually preferred the Pact of Cooperation/Secrecy system. The current system leads to too much ganging up and it doesn't have enough provisions for acts of goodwill. For example, if I help someone out in a war when he asks me to, it doesn't make them friendlier to me. If my 'friend' asks me for something like gold or resources, the only advantage I get from them is that they DON'T feel angry about it. Denunciation and declarations of friendship should be reversible and not permanent, nor should the AI be angry over a war that happened a hundred turns before, or the fact that you WERE a warmonger. From experience, the whole diplomacy system usually devolves into EVERYONE denouncing EVERYONE and no more Decleration's of Friendship still existing by mid-game. Everyone hates everyone. Liberating a worker makes them happy; but liberating a city? NO. And these 'friendship points' should stack, like repeatedly liberating workers/ helping out in war should lead to better relations.
The AI also backstabs me for no good reason, or maybe just over competing for influence over a city state and this sets off a chain reaction where everyone else denounces me just because one of my friends saw reason to. WTF?
So, bring back the Pacts of Cooperation. And Secrecy. Please? At least the AI didn't hate me so much back then And we wouldn't end up with things like a 20 civ FFA
Even better, bring back Civ 4 diplomacy