One of the real joys of Civilization V, a key factor in keeping people playing once the systems have worn thin, is the game's character. Each rival AI isn't just an AI. Thanks to a wonderful combination of art style, animation and voice, they're very human opponents. Instead of just reacting to an AI's calculations, then, you grow to love and despise each rival's moves on a more personal level, hating their aggression and dismissing their pleas. Or, in a best case scenario, revelling in their sadness. Like andsoitissaid does, having gone through and grabbed images of what every single leader in the game looks like once you've knocked them out of the game. For Civ V veterans, it's a delight.
No more bluster and arm-waving from you, Bismarck, you grumpy old coot.
Not so happy are you now, Alexander, with that stupid grin wiped off your face. And your stupid horse's stupid face.
And you, Kamehameha! You...well, I quite like you, so this one makes me feel a little bad.
You can see the full roster here. It's a good look; I've played this game for [censored to protect my shame] and I still had never seen some of these.