Sim City has the following restrictions (features) that have all been stated by Maxis employees:
You must be connected to the internet 100% of the time you are playing.
...... You must connect to Origin to load or save your city (see next item).
...... Games are saved to the cloud (EA Servers).
...... If you're net connection goes down for more than a couple of minutes then all gameplay since last save is lost.
...... The installed game is only half the software, the rest is on EA's Serves so requires a fast, reliable internet connection to transfer data.
...... Other players Cities will influence yours even in 'single player' mode.
...... Saved games once loaded must be saved so you can't change your mind and go back and reload the city.
...... If the game flops and servers are switched off (usually within a year) it will become unplayable.
No god mode terraforming. (This includes how much resources are available and where they are).
No modding allowed at launch (if at all due to online requirements/cloud computing).
No building density zoning.
Buildings may spam along a single road.
Dumbed down micro-management.
Limited population (Max 100,000 Sims per city)
The city tile size is only equivalent to a medium city in SC4, and that is the only size available.
You only get European building sets if you buy the game as a digital download direct from origin.
As I said all these items have all been confirmed/stated by EA/Maxis staff in various interviews so are not guess work...
Considering CitiesXL went down the 'shared online planet' root and it resulted in Monte Cristo Games going bust it seem madness!