One detail that was mentioned on Twitter and that's got me irrationally excited: all your service vehicles are affected by traffic. So if you've got gridlock, your fire trucks can't get to fires in time, your garbage trucks can't pick up garbage, your ambulances can't get sick Sims to the hospital in time. That's huge! Previously they've always been separate simulation layers, but now they're all influencing each other. So a traffic jam (and not just a completely broken network) could indirectly cause a residential building to burn down! That implies to me there's going to be plenty to do as the city gets larger.