Okay well after playing the demo there are a few things I like and a few things I dislike. Hopefully it will give better insight in considering your purchase.
Maps are large with varying resources making game play challenging at times.
It has a detailed street view.
The visual graphics look good.
Zoning tools making interesting developments.
Variety of buildings.
Game is possibly too easy in the general scheme of things.
Some bugs to do with terrain. (Roads being covered by land etc.)
Subscription to the Planet mode
Extra content to the game will have to be bought.
These are only my views however. I am also not aware at having to purchase things like rail links etc. as I believed that would be apart of the main game. Subscription is cheapest at 3 months for roughly £12, cheaper than your average MMO however it needs to be seen if planet mode makes that much of a game play difference.