I spent Friday playing Cities: Skylines and am liking it. You can definitely tell the developer's last game was Cities in Motion, as I spent a good deal of time trying to solve traffic problems and studying interchange designs, something I had zero knowledge of before. The biggest category in the Steam Workshop is custom intersections.
I'm quite proud of the interchange I designed: originally, I had a couple 6-lane streets crossing but wanted to upgrade the "north" and "east" ones to highways while the "south" and "west" roads were fixed in place because of all the people living around there. So I replaced the north and east roads with a raised highway, built a roundabout where the intersection was, and connected the highway to the roundabout with ramps. Basically, I invented a modified dumbbell interchange.
The game isn't entirely about traffic; I'm having a hard time balancing residential, commercial, and industrial zoning (why are you asking for more industrial zoning when half the buildings don't have enough employees!), so I bulldozed all the office buildings stealing industrial workers. A lot of game is about providing transport and services and transport for the services for your cims. Now where am I going to put the new landfill and cemetery we need...
The game is also very forgiving. Players are given plenty of money to experiment and tinker to their heart's content.