Yes, Cities: Skylines has the same problem as practically every city builder: The first few hours are the most entertaining. It's really fun getting a city started, putting those first few districts in place, trying to balance your budget against your urgent need for a fire department, or even just expanding your borders.
But there comes a point where your city is basically a perpetual motion machine--all the parts are in place, and there's nothing for you to do except keep expanding. And I did! I kept building and building and building long past the point where it'd become rote. I just kept thinking back longingly on those earlier, hardscrabble years where unlocking a new set of buildings meant choosing between a hospital and a fire department. By the end, I was unlocking things like airports--and then putting two into my city because why the hell not?
SimCity used to throw disasters at you to make this period of the game a bit more interesting, or at least more "challenging." I'm not sure that's the right answer, but there's no doubt that after a while the feeling of "I'm struggling to build a city" is replaced in Cities: Skylines with "I literally can't build fast enough to use all this money."
There are still some things to work towards even in the late game. They're just less important. Cities: Skylines allows you to unlock unique buildings for your city by achieving certain goals, i.e. building all of the available public transportation hubs will then allow you to build the Transport Tower, "a large office building specifically meant for public transport companies." In-game these buildings only add to the general happiness/leisure of citizens, but it's still cool to break up the skyline with some unique structures.
I also get a sort of thrill from optimization. Cities: Skylines gives you a lot of information about its systems, particularly traffic (which makes sense, considering this is a successor of sorts to Cities in Motion). Trying to figure out how to stop my downtown area from turning into a Manhattan-esque gridlock was an interesting exercise in city planning. One I totally failed at.
Still, don't be surprised if you eventually get the urge to wipe the slate clean and start over. It's good to be king, just for a while. Then it's nice to go back to the small, scrappy mayor dragging a town up from nothing.
Cities: Skylines is a great city builder. I still think my personal favorite is SimCity 2000 but at this point I can confidently say that's more because of nostalgia than because Cities: Skylines doesn't measure up. It does.
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