Anyone got Civilization IV + Expansions?
 

I've asked around and no-one can really give me a straight answer. What do the expansions add to the game for someone who doesn't play the campaigns? I prefer to create my own city from scratch and work from there. From what I understand the campaigns are all "set" scenarios, which is why I don't want to play, am I correct in assuming this?

Anyways, should I be playing the latest expansion and just starting my own custom game from there?