Single player is gimped. A total ripoff.
I strongly advise you to not buy this game. The game is advertised as a single player game, and an MMO. However, the single player game is heavily gimped. To have a full and complete game, you must pay the monthly fee. There are two main points here, let me explain.
First, mass transit. Mass transit has been a staple of every modern city builder since Sim City 1. Well, there is no mass transit in the single player game. What's more, there never will be. The developers have been quite clear on this point. Mass transit will only be available to subscribers to the MMO part of the game, the Planet Offer, or PO.
But wait, I'm not done. Even if you subscribe right now, you *still* won't get mass transit. It's not in the game yet. The first part of the mass transit rollout is buses, and buses will be in the third content pack, to be released around Christmas. Still no light rail, and no word from the devs when it will become available.
Second, trading. Perhaps the most interesting thing about Cities XL is the trading system. Each map has four possible resources on it, food, oil, water, and holidays. The easier maps have a little bit of each resource, the harder maps have a lot of some and none of the others. This allows specialization of cities. For example, a map might have a lot of holidays, but no water. Thus, you would trade your abundant holidays to get water to run your city, and your city would have no polluting water pumps or supporting heavy industry. A specialized city. So far, so good. But wait.
In single player, you can only trade with OmniCorp, at a 4 to 1 disadvantage. So you would need to trade 4 tokens of holidays to get 1 token of water, which is not near enough to support all those holidays you're producing. Above a certain level, your economy collapses.
The solution? Subscribe to the PO at $6.95 a month! Here you can make deals with other players and find a good exchange rate. Unfortunately, even this is borked. The online trading interface (the reason you're paying the monthly fee in the first place) is buggy. Perhaps this will be sorted out later. Next, you need a stable trading partner. What if the guy selling you the water finds a better deal someplace else? He clicks 'Cancel Deal', and your economy is in the toilet until (if!) you find a supplier again.
I suppose I could talk about the numerous bugs and UI quirks as well, but I'll leave it at that. If you're buying this game for single player, look elsewhere. The single player is a heartless, cynical, money grubbing scam to take advantage of Sim City 4 fanatics who haven't had a new game in ages, to get them to part with their hard earned cash. Single player is planned, on purpose, hard wired, to get you to sign up for the MMO part.
Personally, I find this marketing ploy disgusting beyond belief.