Overall, I think this is an absolutely mind blowing game coming from a development team of 13 incredibly talented people. The base game is leaps and bounds above any recent competition and with time will likely be considered the best city builder of all time. There are some things I love about the game, and there is a growing list of things I am concerned about and some need almost immediate attention.
1. Road interchanges are a nightmare to redesign. Terrain height / slope makes it so your interstates / highways have to be awkwardly placed when you inevitably have to do some reconstruction
2. Traffic AI is flawed, and priority needs to be given to emergency vehicles if nothing else.
3. Public transportation needs to have more detailed information in the UI, have easier methods of determining route efficiency, and trains have multiple bug issues that need to be figured out.
4. Not the developers fault, but the way mods are setup in the workshop is a nightmare to navigate through and figure out what's worthwhile and what isn't. It's day three and there are approaching 3,000 items in there and few fall into the categories provided and are lumped together under buildings or intersections mostly. Also being able to add a snapshot of a created asset would be nice so fumbling through a hundred intersections for example, isn't required.
5. A few of the mods that people have come up with should not penalize someone for achievements I think. Some don't really do much other than say destroy abandoned / burned down buildings automatically.
6. This one is a big one for me. One big draw of the game is to see your city in action. It seems if you let any time slip by, bad things happen and just pausing the game isn't the answer because there's no fun in watching everything on hold. The game almost forces you to keep moving instead of now and then being able to appreciate what you've worked towards. Even in the early stages when things are going really well for me, that still feels like the case and I can only imagine when you get into the hundreds of thousands of Cims it gets worse.
7. Provide more detailed information about why industry or commercial aren't getting workers / business. This one might just be me playing poorly, but there seems to be times when there should be no reason buildings are going abandoned when they are.
That's all I can think of at the moment. None of these are that terrible for me other than number 6, and I feel all of them can and will be fixed eventually.