Cities XL is a great game and I recommend it to everyone that likes city-builders.
One of the most impressive things about cities xl is laying down your road network. Unlikely with SimCity's grids layouts in cities xl you can make roads in any direction and also curved roads allowing you to make some rather impressive and realistic city's. Changing roads to a different type or switching them to a one-way is very use full. Also you have a big variety of different types of roads and bridges/tunnels that you can build.
City services are very well implemented. In the old city-builders the services (police station, hospitals, schools, fire station, etc) are accessible by the citizens that are inside the radius (of this services). Now in cities xl things are different, city-services accessibility depend on how well the city-services are connected (avenues, traffic, distance, etc) with the residential areas. For example if you place a college on a main road (such as an avenue, with no or low traffic) they will affect a wider range of citizens.
The economy depend on balance and trade (especially on big city's)
For example if you produce more high-tech industry than you need then the high-tech will make less profited (supply and demand).
A good thing about this game is that you don't really need to pay for the planet-offer the differences between solo and planet-offer is very small (in solo you trade with AI and in planet-offer you trade with other players) maybe the most important thing (for the beginners not for me) is that in solo the trade ratio is 4:1, that means that the solo is a bit more challenging, but still you can build a huge cities (fill up the entire map with skyscrapers) with 10.000.000 population without problems.
Cities XL is a great game and I recommend it to everyone that likes city-builders. Also Cities XL has a potential to become even better with the regular content packs.