There are two more things I miss from RAND: Pollution and Crime. I know both are present in C2C, but I think those are way too complicated, hard to follow and memory wasting.
Pollution
It is often mentioned that unhealth is really not an issue from the Modern era. Sure, health sources need to be balanced, but I really miss the issues mankind face today IRL. I never saw any global warming in game and I think it would be also an interesting twist to require the civs to take care of their environment.
HOW IT COULD WORK:
Introducing a new tag for buildings, improvements and features:
iPollution. Some stuff would have a positive value (Factory, Coal and Oil plant, Industry improvement, Fallout, etc) and others a negative (Forest and Jungle, Forest preserve, Hybrid forest, City parks, etc).
It would have two effects: a local and a global one.
Local pollution: Every city counts all iPollution in its 5 tiles distance including other cities too. If the value is 0 or less, nothing happens; if it is higher than 0 --> decrease health in city with the same value.
Example (with random numbers)
A city in its 5 tiles distance has 2 more cities (B and C); all three has a Coal plant (+0,5/each) and a City Park (-0,2/each). There are 4 Industries (+0,5/each), 4 Forests (-0,3/each) and a Hybrid forest (-0,5).
Its sum is: 3x0,5 - 3x0,2 + 4x0,5 - 4x0,3 - 0,5 = 1,2 health penalty in city A.
If the civ decides to replace the 4 forests with Industries it will be:
3x0,5 - 3x0,2 + 8x0,5 - 0,5 = 4,4 health penalty in city A.
Global pollution: Count all iPollution tags, divide it by 10 (scale to map size?). If the value is 0 or less, nothing happens; if it is higher than 0 --> decrease health in all cities with the same value.
Example:
In the map there are 25 Coal plants (+0,5/each), 25 Factories (+0,4/each), 20 City parks(-0,2/each), 100 Forest/Jungle (-0,3/each), 80 Industry (+0,5/each), 5 Hybrid forests (-0,5/each) and 4 Fall-outs (+2/each).
Sum: [25x0,5 +25x0,4 - 20x0,2 - 100x0,3 + 80x0,5 - 5x0,5 + 4x2] /10 = 3,4 health penalty in all cities.
Local and global pollution in city A would be 7,8, that's quite a big
penalty
There would be several ways to decrease pollution:
-Green civic could halve all positive iPollution values at the cost of a High Upkeep
-Shielding buildings make the city immune to pollution at the cost of maintenance.
-Build Hybrid forests and other improvements and buildings that reduce it.
Crime
Just like revolts and rebelliousness, crime is also a factor that produces enemies to a civ among its own people, but in a different way of course.
HOW IT COULD WORK:
Every city would accumulate Crime points every turn through different factors: Buildings (Jail, Police station, etc), Population, Unhappy citizens, Spy and Priest specialists, Golden age and Anarchy, Civics, Units garrisoned in city.
The accumulated Crime points would work something like Espionage points for barbarians. When Crime points reach a certain threshold - the value is equal or higher than a given Spy action there is a 10% chance every turn that that Spy action happens in the city as if it was performed by the Barbarian state. If that happens the actual Crime points are halved.
So with a low crime rate things to happen would be Unhappiness or Unhealth for some turns, than Barbarian culture would spread, buildings get destroyed, production sabotaged, etc up to the very high crime levels when nuclear device is planted or anarchy is spread throughout the whole civ.
I know, I know... the devs don't want new features, but I just had to put out my ideas here