You may ask, with so many sequels Cities XL is a good game? Well, it depends on how you look at it. You can check my review on Cities XL 2011 here. I did not play Cities XL so I can't say much about it.
Key features like gameplay and replay value were left behind in the «to do list» of the developers and one might even say Cities XL 2011 was released in beta stage. The game did not feature a Campaign of any kind. You can address the «Single Player» of Cities XL 2011 as a sandbox mode, something you would try after completing the non-existent campaign. Although it came with various maps, all very different, each one with certain resources, from oil to fertile areas, a single strategy would suffice for every map. In fact, I don't think there's more than one strategy here. The economic aspect of the cities were poorly developed - it's very hard to keep your budget on the green line. Things like public transports being free, or oil extraction fields giving loss rather than income do not make much sense, in my opinion but the biggest flaw of Cities XL 2011 was its incapability of taking advantage of multi-core technology. As my City was getting bigger, the game was becoming slower and lagging because only one of my cores was processing the information, so in the end, the game would become unplayable and it would be hard to reach a large city.
Now, what is expected of Cities XL 2012? I have seen, on the forums, lots of players saying multi-core is a must and not a single word of the developers about it. When Cities XL 2012 was announced all that was promised was new maps, weather effects and more buildings variety. It was also mentioned that owners of Cities XL 2011 will be able to upgrade it and get Cities XL 2012 at a discount price, which makes me wonder if Cities XL 2012 is really worth it, specially considering it seems more like a patch, rather than a new game.
I will not acquire Cities XL 2012 if it doesn't come with multi-core support or if it doesn't offer a single player mode with at least something to guide you, rather then just the free mode it offers.