Didn't see the request a mod thread before, so cross posting this from the discussion forum.
There's several areas that I could touch on, but one specific change that I'd like to see is a more strategic resource driven game.
Raidable / Tradable / Physical resources
I would love to see the resources as physical quantities in the game that actually have to mined/developed/collected in one place and moved to another for storage and processing (building of units/buildings). This would allow for mining colonies and huge industrial cities and create a far more strategic element to the game than what there is now, and would create a more balanced system for cities -- cities that have a strong industrial base would be larger and more important than ones that are further away or are just developing.
CUMULATIVE
Resources would be cumulative by turn. So, an iron mine of 3 would give three iron per turn, which would have to be shipped to a city for storage and process (unit and building creation). (A limited amount (say 10) could be stored at the point of origin).
COLLECTION/MINING/HUNTING etc.
Resources would be physically collected at mines/camps/wells (which would have a limited storage capacity)
USE
Strategic resources would be still used to create new units, but also used to repair (heal) damaged units and buildings.
Luxury Resources would be consumed based on population. 1 luxury per population. Consumption of LR would be at closest city. The more resources, the happier the empire. Cities with no resources could have them shipped in.
STORAGE
Cities would store excess resources in specialized buildings (granaries, smithies, etc.).
TRANSPORT
Specialized transport units could be automated (like workers) so as to avoid the micromanagement nightmare that so many people complain about, or could be given specific Trade Routes.
TRADE
Resources between nations could be physically traded and shipped - so for example when Babylon pays you a 100 gold for your wheat for 30 turns, there would be physical transport of wheat from your granaries to Babylon.
RAIDS
Low on resources? No problem! Raid your neighbors supply lines and capture their transports! Cripple their economy by disrupting their strategic resource industry and create discontent in their cities by blockading their luxury imports!
BARBARIANS
Barbarians can actually collect booty now. They'd raid mines and take the resources supplied there, and capture transports full of supplies. When you capture a barbarian camp, you collect the extra resources!
CAPTURE CITIES
When at war, along with disrupting enemy supply lines, when you capture one of their cities, since resources are stored there, you get the spoils of war. It could be just few barrels of oil, or it could be hundreds.
ADJUSTMENTS
Resource production would obviously have to adjusted so as to avoid insane amounts. Each resource could reasonably provide 1 resource per turn. Resources no longer needed (such as iron in late game) could be shut down, or used in conjunction with other resources (say oil) for the construction of modern units and buildings.
LIMITED SUPPLY
Resources run out. Especially resources like iron or oil. Each resource would immediately start depleting from a random number (10 to 1000). When it runs out, a new supply would need to be found. This would apply to both strategic and luxury resources.
Conservation Tech
New Tech for the Modern Era - Conservation - this would extend the life of resources for another 10 to 1000 turns.
RESOURCE DRIVEN TECHS
Technology is resource driven. If you have access to Wood (Forests), you can research archery. If you have access to Fish/Whale, you can research Sailing. If you have access to Stone, you can research masonry, and so on. Once a new tech is developed, the resources for the next tech advancements become available, so the tech development arch is not disrupted. But you have to have the resources to advance down the tech path. This will allow for different civilizations to advance at different rates based on what they have available to them. Some will outright stagnate.
EDUCATED UPKEEP
Tech knowledge can erode leading to a dark age. Just because you know how to do something doesn't mean that you will
always know how to do it. The larger the population, the larger the amount empires will need to spend in the upkeep of knowledge. Certain Culture branches, like Tradition & Reason, would get an advantage in this area.
Ok, that's it. Feel free to shred it

~S