One thing I definitely think Civ3 is lacking in is a proper relationship between people and ruler.
I think that the ruler is responsible for too much. He builds Settlers, Irrigation, Mines, city improvements... some of these things (in fact quite a number) are actually built by the people. Unless they exist under a government where the ruler is much more in control of the economy.
But one thing I suggested waaaaay back was for rural population... and it would be a population that would expand on its own. Every tile would have a value... say 1 through 10. 1 being the least desirable... say... Desert.. and 10 being the most... say Sea Coast with a River. Your population would naturally expand on its own to the surrounding squares and would gravitate toward the most desirable land... Rivers and Sea would be the first spots, or lands that have roads constructed on them.
If your people are seafaring, they may skip over undesirable squares via the ocean and move to more desirable squares along the coast.
New cities would pop up once a tile's population reached a certain amount, and the city's appearance usually be in an area that is the hub of transportation... river intersections, road intersections, good deep harbors, etc.
So your people can be seafaring people who survive on fishing, shellfish, and so on. You can be people living on flood plains and growing crops (or terrace farming too)... or you can be a shepard culture living off of sheep, yaks, cattle, or whatever beast happens to populate the surrounding area. Of course, having any one of these does not exclude you from the others, it just means that tile for tile, there are more tiles being exploited for this purpose.
And this economic basis is one of the determinants in their choice of religion. Agricultural cultures TEND to have polytheistic religions, while shepard cultures tend to be monotheistic. Sea cultures are somewhat of a toss up... but the SEA sort of presents that awesome power that might be associated with one god only. It has to do with the fact that there are many factors involved in farming, so therefore there are many gods in control of these factors, while in the shepard culture, they see the logical role of a higher being as a shepard... "The Lord is my shepard..." that kind of stuff... the Middle East has been afterall very strong in the herding business.
But, yes, the population expands and moves into these new areas, but the ruler does not necessarily hold control over them... he/she must gain control over them by either deifying himself/herself, or military control, or a combination of things... but whatever path he or she chooses will have ramifications in the future because it sets precedents.
And there should be different classes: noble, middle class, lower class. Basically, the middle class comprises the artisans like black smiths, potters, so on and so forth. The lower class, in the beginning, is largely peasants and so really doesn't exist much in the cities, but as industrialization begins, then there's a much larger labor class in the cities.
The ruler, then, is responsible for building government buildings like military quarters for the troops, governor's palaces... and I guess in the beginning, the leader would be responsible for temples and such as well. But later on, edicts and government choices will eliminate the ruler's involvement in religion (should the player go that way). And the ruler is also responsible for constructing roads, harbors, and military fortifications. Barbarians should still be a big concern.
Basically, in addition to worrying about OTHER civilizations, the leader must be concerned about maintaining his own power. A balance must be maintained between the nobles, middle class, and peasants. If one is favored too much over the others, it could lead to political turmoil, especially when a player starts adopting a more democratic society. And there could also be civil wars as political factions form, or if outlying regions decide to declare independence.
So we remove a lot of the player's concerns by making expansion the job of the people, (although the ruler, in early government types, can order certain places to be colonized first if he so chooses to gain control of valuable resources, or they can send military troops to occupy a region).
In terms of war, the ability to wage war can only go as far as the ruler's pocketbook. Treating the middle class well, especially in the later game, is VERY important because not only do they do much of the work in creating the military weaponry and equipment, but they also make up the financiers for the royalty. On the other hand, in the medieval era, focus too much on the urban middle class, and the provincial nobles may not want to contribute troops to the cause.
Edicts can be declared so that you can get a big boost in morale and loyalty from your people by declaring certain religious elements expelled (or exterminated) from society.... like in the Inquisition or jihads. But the price you pay is that you eliminate much of your middle class, which when war breaks out, may lead to big problems.
But there are these sort of foreign bankers to turn to, who charge ridiculously high interest rates, that can snowball. If your funds drop too low, and you run too much of the society, you could have a French Revolution on your hands... especially if you have to start taxing people who previously enjoyed little or no taxation.
And there are other edicts... like religious tolerance (as opposed to a Kulturekampf or Inquisition). Or edicts on the allowance or forbidding of slavery. Creation of a constitution... or the suspension of a constitution, declaration of martial law. All of these have very specific effects, and the longer they remain in place, the harder it is to overturn them.
And the governments would work in sort of a three-fold manner.... there would be the governments, Monarchy, Feudalism, Republic, Dictatorship... and then there would be economic standings... Laissez-Faire, Protectionist, Command, Socialist, Communist. And then levels of social control... Anarchist, Free, Police State, Totalitarian. (Note: I'm not sure about the labels for all of these).... but the thing is that, of course, certain forms of these things will not work with others. It's hard to have a Laissez-Faire Totalitarian Feudalism... so certain ones would be grayed out if you chose them... but also sometimes its hard or even nearly impossible to change some of these depending on your people. And sometimes, they may change them FOR you..
Basically, in the case of the market... the populations will freely trade resources with other civilizations unless you or the other civilization put the kaibash on that. And you can make certain goods hard or impossible to attain from another civilization. There would be prices for everything that fluctuate depending on accessability and production output. Unlike in Civilization, one supply will not be enough to support an entire civilization regardless of the number of cities. Also, certain goods are manufactured... Pottery, Jewelry, Clothes, Steel, Cars, and Rubber if you learn how to make synthetic rubber.
Also (and I've discussed this elsewhere) but I think it would be good idea if roads, railroads, sea, rivers, and canals had a carrying capacity... that you can ship goods along these routes, but you can only ship a certain amount... say 10 units for roads, 20 for railroads, 25 for sea or something like that. And the greater, the distance, the more the commodities cost. The result is that it makes these serve a much bigger function that giving slight trade boosts and shuttling troops. It also enables submarines to target sea lanes and cut off valuable supplies. All seems very complicated, but as I said before, the computer population would be in charge of most of this unless you choose a command or communist economy, in which case, you run the show. The only thing the player has to do (regardless of government) is to ensure that the sea lanes remain free of enemy privateers, pirates, or belligerent navies... and construct roads and railroads and make sure they're clear of maruaders, bandits, and barbarians.
Well, these are just a
few ideas I have if I were making my own game...
But like I said, it depends on what you want to do... I've got A LOT of suggestions, most of which would take the game in a very different direction from Civ... I really wouldn't want to get involved in the creation of a game unless I felt like it would be an improvement in my eyes.
Maybe not. 
