Domination.
At least it was from Civ2 until Civ5 G&K. I always felt that I did something wrong when the map wasn't painted in my color at the end of the game. I really loved the war aspect of the civilization series!
I don't know whether or not I will be able to maintain my love for this. Honestly, I haven't played enough games with BNW to make up my mind here - but so far, I have got the impression that the domination game was massively hampered in this expansion. Too much to be still fun? I don't know, right now. I hope not...