I wish I had time to write all of the ideas I've had or at least second all of the good ideas I've read here that inspire me, but here are some that I felt should be posted (sorry if some are repeats):
World
- Realistic spherical world with more dynamic changes in geology; over 6000 years, islands vanish, mountains grow, rivers change dramatically, deserts appear and disappear (In 4000 BC, most of the Sahara was actually lush tropical grassland.)
- I'd like to see multiple zoom levels on this world, so it's possible to view just a few cities up close or your whole country, or the whole planet.
- I'd love to see cities get much larger, from tiny hut settlements to huge metropolises. Settlers could be much cheaper, and cities could start out much smaller and have a risk of dying out on their own. Also, I'd like the city graphics to represent what is in the city, not just the size of the city. Even if this is not done for ordinary buildings, I think it should at least be done for wonders. Large wonders like the Great Wall or the Pyramids should be visible on the main map (outside of the city icon).
- More natural disasters! All the time!
Religion
- I don't think religions should be restricted to what Civ you use, like the traits are now. Civs should be able to choose their religion, or have it changed through interaction with other civs. You could maybe set a "state religion," but with distance from the capital that power could be less effective (like corruption gets worse farther from the capital) so that cities that are far away from the capital and close to another powerful religion could be converted to that religion (and maybe that will aid in that city doing a culture-flip). I liked EdwardTheKing's religion post, and think that's a great idea, except that I just think religions should not be linked to specific civs, and that civs should be able to change religions like governments. Religion should be something that can be influenced by the player (like building temples and imposing a state religion) but is ultimately determined by the citizens of your empire.
Government
- Governments should be customizable, not just flat all-encompassing rules. There could be a government "template" like Republic or Communism or Monarchy, etc., but it should have many little facets that are selected by the player. For instance, free medicare (which could increase happiness and growth but cost money), free market vs state-controlled market, representative government vs. non-representative. That way governments could change gradually over time, and change would be more frequent, rather than having one or two major revolts in an entire game.
- Like I stated about religion, government should be influenced by the player, but ultimately determined by the citizens. Obviously a fascist government would not be effected by citizens, but a democracy would be very effected. The citizens could demand certain government aspects (like petitioners do in Sim City) and you could choose to either appease them or oppose them. Rulers who do not listen to their citizens would face more riots and possibly be overthrown or have a civil war or something like that. There needs to be more stuff like that in Civ.
Trade
- Everything should be tradeable, from food to goods, to shields, to military units.
- I liked the way trade routes worked in Call to Power 2, with illustrated routes on the map, and the option to pirate them. Also, I liked that the distance of the route provided a trade bonus.
- You should be able to buy more resources for more happiness. For instance, if China is selling me spices, I should also be able to buy French spices, and Indian spices. Maybe extra spices give less of a bonus, but I think they should still be trade-able.
- There should be a lot more resources, and maybe increased value for having multiple resources. Say for instance I have saltpeter. Maybe 1 saltpeter gives me the ability to create musketmen in 5 cities but to create musketmen in 6 to 10 cities, I need 2 saltpeters. More resources should pop us as time goes on, so that once gunpowder is invented, there's a few saltpeters, but by the time rubber has been discovered, saltpeter is all over the map (sort of how Civ3 justifies that infantry doesn't need saltpeter because by this time, it common all over the world), only this illustrates it in game mechanics rather than just fading out the need for it. That way a tiny island civ would have to either buy saltpeter or buy the actual military units, but either way it's more realistic and illustrates how civs are all dependent on one-another.
Production
- I definately want to see the option to build buildings at the same time as military. This allows for more types of buildings and more types of military units, making the game more versatile.
Civs
- I want to see the option for Civs to change names mid-game. Civs can split in two, you know? For example, say you play as Rome. Mid-game maybe your civ has a revolt and halfway-through it splits into Rome and Byzantines, forming a new Civ. Well eventually you decide you want to rename Rome to Italy. Same country, you just gave it a new name. Why not? You can rename cities afterall.
- Splitting of civs is a big thing for me. I want this to happen a lot, even if it's just one-city rebellions that need to be quashed. Each Civ could have a list of names of civs that can form from it. For example if you play as England and there is no USA on the map, say England gets to big... it could split into England and the USA. Then later it could split again -- in to England and Australia. Or Canada. You get the picture. This allows for more playable Civs. The civs can even share the same city name list or have their own new ones.
- Along the lines of splitting civs, I loved that nationality played a part in Civ3, but what if the nationality could revolt and change back into a civ? Say again that you play as England. Say you conquer India completely, eliminating it from the game. But then say that you treat the newly conquered territory really bad and they revolt and try to split from you. Rather than change into the USA, since there would probably be a majority of Indian people rather than English people in the cities, it could split away and turn back into India, bringing the civ back into the game.
- Allow 1 golden age per era, not just per game. If the science method mentioned below is implemented, this would make golden ages more random and less in-the-hands of more experienced players.
Science
- I love the idea of science not being controllable. You just get to pick the field (like military, cultural, civil, social, etc.) If this idea is implemented than you could even base science on resources, like no shipbuilding if you dont have wood, no guns if you dont have saltpeter (you'd have to trade for these resources to discover the tech on your own). That way civs that lack in some areas could excel in others. Say you're an isolated island civ and you don't know anyone else... why on earth would you discover advanced military techniques if spearmen suit your civ fine? You could just research advanced literature, government, and things like that. Then later if another civ meets you, you could trade civs, or they could use their advanced military to try to conquer you. You may have been the only civ in the world to have an advanced government at that time, and the information could be lost to the ages when you get conquered. Things like that have happened throughout history.
Well that's all the time I have to write right now, I'd love to keep going. I'll post more later I guess.
Hell the advisors weren't very useful, but neither are civ3 ones, but at least the civ2 ones were entertaining 
