personally i would like to see some of the concepts of colonization integrated into civilization. for example, i thought the founding fathers were great. i think it would be cool to have founding fathers instead of the small wonders, and have them appear as a result of a variety of factors. for example, if a particular city has huge science output, then, say, albert einstein would appear in the city. then, like a leader in civ3 he could be moved and whatever city he was fortified in would get some sort of bonus. then, after an alotted amount of turns, the person dies and the effect goes away. i think this would be a cool feature because it would reflect the great influence that individual people have had on history. also, while im on the subject, it would be interesting if every founding father had a positive and negative side which manifests itself depending on what sort of government youre in and other conditions.
i know might be wishful thinking but heres a few ideas of "founding fathers" who could make the game more interesting.
lenin: appears under monarchy when war weariness sets in during an industrial age war. effect: allows conversion to communism in 1 turn, but will create unrest if monarchy remains in place.
caesar: appears in ancient times after a certain military accomplishment. makes armies stronger and decreases shields to build units, but if you are in republic or democracy he creates civil disorder unless you change to monarchy.
castro: like lenin but in the modern age, and also makes guerilla warfare unit (like in civ 2) more powerful.
etc, etc.
it might be worthwhile to make the founding fathers like unique units so that they contribute to the differences in playing as different civs.
also, id like to see many more forms of government, that you could potentially chose, each with a unique unit and building associated with it. let me know what you guys think of this idea.