At first it was a mess, game not unlocking for multiple hours, servers down, queues, weird error messages, being unable to play with friends, then they disabled the fastest speed and leaderboards/achievements, then a week passed... And now Sim City is playable, more or less free of server woes and other technical problems that have close to no bearing on core design discussions. Of course one could argue that the fact that Sim City needs to be always online is a core design problem but I think that by itself it wouldn't have been if the servers were on from the start with 0% errors and problems related to the technical issues.
With that long intro paragraph about how the game itself is not playable and that technical problems shouldn't impact gameplay, what about the game then? Is Sim City fun? Yes. Is Sim City interesting? Also yes. Is it a good city simulation? Not at all.
They tried too hard to be two things: A toy and a simulation
How would I simulate employment for a city of 100.000 inhabitants in a videogame? I would take the number of jobs available and the number of people, if there are 100 000 jobs, it's all fine. Maybe add some complexity, like tiers of jobs and tiers of workers if you need it. How would I display that in a game? Probably not by showing all of those people go to their jobs because it would take insane resources to display all of that in a realistic fashion. Maybe it would be possible with 10 people, but Sim City tries to do everything I just talked about, no matter what you try to make as a city and it fails miserably. Everything tries to be simulated as a toy and it falls flat to do both.
It's not a great simulation because the engine couldn't support 'real' interactions between sims and their jobs/education/services. You would need to have your sims actually live somewhere and actually want to go somewhere else they precisely have to, like work or school. Their solution is to have them go to the first available spot by the shortest route and come back to the first available house. It's not a good toy and it's not a good simulation either. It's not a good toy because you can't make your sims do anything logically (they'll get stuck in weird loops, take high-traffic roads when free ones are available, complain about things that won't make sense) and you can't simulate the town logically either, because if your police coverage extends to a part of your city and a crime occurs there, maybe your police won't be able to get there in time because the actual cop car will be stuck doing loops on the highway.
Even worse is when EVERYTHING is working within this framework, power, water, sewage... It means that a little blob of electricity needs to go to every house for them to have power, no matter if you have tons of surplus or if your grid is well designed, if someone lives at a weird place where the roads are 'too complicated' for the game, they might not get power at all.
How I would fix this
This is tough nut to crack, either by removing the toy part or the simulation part, but that would mean reworking the game and rebranding it, potentially. Removing the toy part seems the easiest way for me, you remove the need for actual sims to go to places. You still do it for show in a random fashion but you stop pretending that it matters to anything. Electricity won't need to go to places to actually power them, water and sewage the same thing, as long as you're connected to the grid and there's enough power, you're fine.
Removing the simulation part would mean renaming the game to "Sim Town" or something and then scaling down the size of your cities even more but making the actual sims more intelligent and realistic. It could be a neat idea to have a little city where each and every person has their own job and money and goes shopping and you need to balance everything out so everyone is happy, but you can also focus on the personal happiness of individual people so they get better at what they're doing and it makes your city grow in quality. Or something. Both ideas are fine to me, the first one would be to 'fix' Sim City, the other to make an actual great game with the GlassBox Engine
The data is bad
"Crime has the upper hand!" claims the police tab of my city, build more car cops and police stations, it says. I look at the numbers and they look something like 0 crimes perpetrated, 5 out of 5 criminals arrested. The crime map shows me that there are certain zones in the industrial sector that are more risky but they are well-covered by my police station. After a while I notice certain abandoned buildings show me 'Too much crime' as the reason why people left.
Same thing with zoning, they always are asking for more residential or industrial (I've never seen requests for more commercial, personally), I build more residential zones and I still get the flashing icon to remind me that I need more workers. Do I? Is that the simulation side of the game that's trying to warn me or the toy side that's trying to work within its limitations and is breaking around the edges? Not being able to act upon the given data because you're not sure if it's reliable feels terrible, I've stopped caring when my health system warns me of impending doom because no sims died and my clinics aren't even full capacity yet.
Another instance where the data is bad occurs when you're trying to lay down stops for your schools buses or public transit, even if you cover the whole map with little stops and your whole grid is lit with coverage, even if you have bought the maximum number of buses, people will complain about long wait times and inefficient transit. 90% of the time this will be because buses are stuck somewhere and not because you have planned your city wrong. Why show that data if it's not used?
There's also talk about how some very basic data is also flawed, meaning that the population represented by the game isn't the actual real number, more like a value inflated by a factor of 8. I'm not sure why they did that because the 'fake' people can't really contribute to your city in any way since they don't go to work or to stores, no?
How I would fix this
Show accurate data. Don't show ideal pie-in-the-sky data like you do currently. In my transit system example, instead of showing the 'theorical' coverage of your bus stops, show the actual one, then you'd see that buses only go to 3 stops and then spin around your city for no reason. Same for your fire coverage and police coverage, if the cops only do a small loop around the station then come back and only arrest criminals in that radius, don't show the whole town as covered, show only that small zone, then the player would know that there's a problem.
As for the zoning and population issues, I'm not sure exactly how they impact the game yet and making any suggestions would be unwise.
Always online multiplayer
Games that play fine in single player shouldn't need to be always-online, that's for sure, and Sim City is a weird case to call a 'MMO' like some people in the dev team did. With the small size of the regions it's not really massive and the player interactions are asynchronous at best. The idea that one city can send water and power to another and that shoppers can move back and forth is nice. The idea that you can send money to other cities or materials is also neat, but it's not explained properly how it works. Sometimes you send things to other cities and it never gets there so it's a net loss for everyone. Whenever the server glitches, you stop receiving water and/or power so if you rely on your neighbors too much it might bite you back..
The fact that cities are saved in the cloud is also a double-edged sword when you get an error message and need to restart your city completely. Or that the servers are down - and of course it keeps working - but this isn't about the always-online technical part of Sim City but rather about the sacrifices you have to make for the game to work that way. Smaller towns, the inability to build everything inside one single city that should theoretically be offset by the fact that you're playing with multiple people and they're all contributing to big projects such as airports and archologies.
It doesn't work because you can't easily see what it's supposed to do and it's frustrating because it's the only choice you have. There's no big 'Multiplayer' panel in the UI that shows you what you're getting and sending and the money you get from your friends, there's no 'project' panel that shows the progress your archology is making in real-time. It's also weird that power and water from other cities aren't bound to the same rules as power and water from your own city, they just spread magically everywhere, it's not a big glob coming from your highway or anything.
Also I have some more confusion related to those systems, can your people really leave to work in other cities and vice-versa? In that case, why am I always asked to zone more residential? Couldn't people from other cities come visit mine to work there? It should fill any unemployed spots in my town. Couldn't you make a town mostly of residential zones and a town of industrial zones and connect the two without having any pop-ups about poor city planning? The game is supposed to be a multiplayer one, have it work that way or think about the steps that brought you there.
How I would fix this
Add an offline mode, increase the basic size of the cities, add more UI options in multiplayer to get info on what's going on, region-wise. Show all of the available data regarding to the multiplayer and how it's helping you, maybe then players wouldn't be too mad to play this game online if they knew what it gave them.
All and all, Sim City is a thing that I might play from time to time if they fix some glaring problems with it like the way the roal tool is broken, or airport or other small things that are rather technical. That being said, I don't think that I'm going to buy any DLC they release for it and I'll never see the new Sim City as a deep simulation game, more as a pretty toybox.