A very good city simulation.
Cities XL 2011 is one of the good ones.
There are an array of different buildings to build, and the developers have done a nice job with a clever system of slowly advancing the player's ability to build larger and more complex commercial, residential, and infrastructure buildings and facilities, using various milestones such as population and wealth. And it is done in such a way that you don't feel limited by the build restrictions - the progression feels natural.
Production values and graphics are good and the interface is fairly intuitive.
There isn't a campaign or mission mode (which may be good or bad, depending on your taste). It's pretty much all sandbox, although there is quite a nice selection of different terrain and geographic map types to choose from.
In terms of in-game assistance, the game doesn't treat you like a mayor, like some city sims, with "advisors" giving you hints and suggestions. You are pretty much on your own to monitor various statistics - again, a good or bad characteristic, depending on your preferred game style.
A couple of annoying features: unless you are zoomed practically to street level, there are virtually no sounds. So, if you are like me and you play most of the game from a greater altitude, the game is virtually silent.
Also, I have very good hardware and the game still lags as you pass through various levels of zoom or otherwise use the interface.
All in all, definitely worth the money, and although the bar is pretty low for these types of games, probably one of the best city simulations currently available.