I'd be more interested in an expansion or update that further develops on the social aspects of city-building.
We really need to start focusing more on the simulation side of the game rather than the eye-candy. More specifically, I think it's about time citizens get revamped. They are way too dull to follow around once you're finished your city (which I argue is the end-game content). The addition of social demographics, wealth and citizen needs would solve many of my grievances with this game.
Let's look at how leisure function in this game. A park, a playground, and a skate park would have the same effect on the entire population. In real-life, a person with no interest in skating probably wouldn't care about a skate park; a household with no kids wouldn't care about a playground. With the concept of demographics, each park would affect a different part of the population. Parks would affect regular citizens. Playgrounds would affect kids and families with kids. Skate parks would affect people that have skating as a hobby. That way, it would be encouraged to have a variety of solutions to satisfy the population instead of just one cure-all. These demographics can be expanded into a set of interests that a citizen can have that determine their favorite forms of entertainment; sports, gaming, books, movies, etc. These interests could also influence where they may work.
Similar behavior would also apply to citizen needs. Citizens would need to supply themselves with food, entertainment, clothing, general goods, etc. This would make your commercial district not only just look diverse, but feel more diverse, as gas stations will no longer have the same effect as a restaurant.
With this implemented, you would have to closely examine your population and gauge their interests, and figure out the most appropriate area to place certain types of buildings. This would lead to much better and more engaging gameplay than just plopping any building wherever and achieving the same effect. And maybe you'll start to care more about your citizens as they behave more human-like, and not want to just drop a meteor on them just because you can.
All of this tied in with a deeper economy system;
- Make it so that cims have to get a job. If they remain unemployed for a period of time, then they should be forced to move (unless they are pensioners, kids and teenagers, or anyone that lives in the same household as someone who has a job). They shouldn't be able to live their lives without working.
- Have the cims require access to stores. Honestly, how do they live without needing to buy food?
- Have buildings only be functional when enough workers are present. This could also solve the issue of cims not needing to get to work at all, and drive the player to make sure they get there on time. Cims should also lose their job if they miss work too often.
- Wealth classes should be introduced to make the economy more dynamic. Cims who work higher positions in their workplace would have more access to higher quality goods (in this case, sold in lvl 3 stores) than poorer cims.
- In order for this to work well, a functional day/night cycle is just as important. Cims must have a consistent workday/weekend schedule to simulate these effects correctly. They work during the morning, return home in the evening or go shopping or visit leisure venues, and have free-time during the weekend. Some workplaces (emergency service buildings for example), would have some cims working nights and/or weekends.