I never liked vassal states in Civ IV, and I'm feeling city states make it much easier to win in this version (especially diplomatic victories). Not to say they are a bad idea, but their benefits are a bit too much. People relying on maritimes for food (a crutch, if you ask me), getting bonus culture for culture victory, buying votes for easy diplomatic victories, or getting free units to help the warmongering.
I've seen some comments about this version of Civ being too easy. Maybe turn off the city states then and play old style Civ where your enemies were just barbarians and other civilizations.