There appears to be an issue with the game installing at v1.0.3 instead of the new v1.0.5. This can be resolved according to Paradox to make the Cities Skylines Steam install grab the latest v1.0.5 patch. Follow these instructions.
If you see your game is this old version, or you have some strange problems, please exit the game and verify the integrity of your game cache via steam.
EDIT Running a laptop and have performance issues? Make sure you’re not using the integrated GPU (this is especially a potential problem if you’re running Windows 8.1)