You start the new city with excitement. You play more and more way to see how is your achievement unlocking. Following each Milestones. Then you find some achievement are really hard to reach. About 12% of achievement need a long play and learn your city mechanism. So these player developing to another trail, if they not just come fast and leave.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=409335954&searchtext=achievement

You must have playing Cities in Motion, I guess.., and it really effect the way you design your city. You loves trains. Cities Skylines even have achievement name 'Cities in Motion'. Train (not Metro) is a good way to connect two or more separated cities together. But some players even cutout road between cities so they can build more trains. They must really love trains. Not to mention with Bus, Taxi, Ship, and Plane. I find Taxi is the hardest one to build, with benefit...
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=408643569

You like create asset that made your city unique. You design some powerful assets that support your city, feel that large city are too hard to play without using the assets. You download asset and share your creation too. Some people are also using mod. Mod that would made their cities less challenge but gain an exceptional nature.
But do not use too many mods, especially the mod that conflicted with another. So your game would remain stable.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=407800369

Update 12/05/2017
Look like the new strain of players are coming. Some 'Micro Organizer' are not only sharing asset, they made real-world building. And when more than one copy of the same building name are made, the best version are selected by us (the community). Their work are so good, making me think "they must really love what you are doing". Could it be that they're even an officer at the building they live?
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=683428358&searchtext=baiyoke

(People are researching how to play computer game?! Yes, they do. You know.., it is not as intense as scientific researchers do.)
You like realistic city and see how can it compare with the city you live. Some mechanism are so real, some are not. (Since they would made the game, too complicate or burn your graphic card).
Or you may be the people who were suffer from 'Death Wave', and you desperately search and re-search the way to cure your city. Then, they are some nerdy city-builder writing guide how to reduce Death Wave. And, I have READ them a lot.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=578759936
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=425513385

You are a rare major that prefer to continue on your favorite city, you try not to reload the game. Of course you have play more than one cities. But at some point, you decide to build a fairly large sustainable town. The town that even remain healthy for hours without you monitoring on it. It is good to see if your city can last on, even after there are not much land to expand more zone.
And now that the 'Natural Disasters' expansion is on the play, you can test your survival skill on Scenario Mode too.

5a. Low tax survival
More Survivalist is appearing, player test how to remain positive income on very low tax level.

You like views. You took screenshots of your unique city. You might know nothing at all about know to maintain city, but you share landscape screenshots to the community. Some people will look at your work, and they just like it. On the another hand, you design map, build a functional town (it doesn't need to be big). When your town is completed, people laying curved road, they adding several assets . Then, the system include real-world building. Your screenshot becomes an artwork. Every trails from any player type you visited, they have will, they can make you a nice Photographer. Photographers really do contribute creativity to the Cities Skylines Community, we liven up the site.


Here is the city I play on.



"Not so impressive huh? Not even a single modified asset in. Well, it's a growing city. Hopefully mine will be an Artwork someday. Or maybe not." XP

Update 17/01/2020
'Micro Organizer' are finally cross-over with 'Photographer'. A surprise. Just a few players but elite, they are making so much effort at decoration. The cities must not be only a beautiful view. They can't be too beautiful. So the 'World Decorator' create their city using Google Maps, so as to reflecting how their city are doing. How well-being of your city achieve so far; are preferable with the city which player -your friends- live in. "Thank you"

It's been a long-time since 'Cities XL', I'm waiting to see if a virtual city can partially predict a flaw in real city. For an improvement. Now that, the hard part is about edge of each city we create. It's won't connected. But look at what Cities Skylines is making, it like a white-hole, out of nowhere. Who know? Even when these game expire someday, we could export an asset to Google Map for an engineer reservation. We might won the world.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=774855825