The diplomacy of Civ V is a joke and the Fall Patch has unfortunately proven that Firaxis does not understand this and will not be changing what is a horrendous model to the core.
Diplomacy should never have revolved primarily around who is a warmonger or not the way it does now. There is no basis for this in terms of realism; there is no basis for it in terms of gameplay. It is an unfun mess that leaves the player seeking for ways to work around this artificial obstacle of being branded a warmonger rather than playing the game (avoiding conquering a civ's last city, anyone?). World affairs never were dictated by pointing fingers at 'warmongering menaces to the world'. Did Rome attack and destroy Carthage because Carthage was a dirty warmonger? They did it to secure their own interests in the Mediterranean - because Carthage was a competitor, not because Carthage was OMG BAD GUYZ. Same can be said of virtually every conflict there's ever been.
In Civ V, diplomacy is taken to finger-pointing kindergarten level. Practically the only thing that really matters diplomatically is whether you conquered some random city or not, in case of which you'll be hated for it by every nation on the globe, even if it happened hundreds or thousands of years ago, and regardless of if you had otherwise good relations. It is, excuse me, idiotic. The needs and current statuses of nations take a second priority to resenting some unfortunate civilization for what happened hundreds of years/turns ago (while at the same time being perfectly fine with seeing some other civ that could threaten their very existence running away with the game). If the real world worked like Civ V's, we'd still be bombing or at least 'denouncing' Germany.
They could have gone with a sane, adult model like the one used in the Europa Universalis series, which manages to feel both realistic and relevant. Instead, they've perpetuated the "warmongering menace to the world!!!!111" again, the Fall Patch once again shaving off just a tiny layer of the worst ramifications of a broken diplomacy model when a total rework was required in the first place.
There's my thoughts on Civ V's diplomacy, the single weakest aspect of the game.