Two weeks after first announcing the title, Zynga has finally launched its fourth, and most ambitious, Facebook game of 2010: CityVille. The game went live just before midnight last night.

Our preview of CityVille explains most of the game’s features: shipping and goods production, farms, franchises in friends’ cities, and a thorough list of the best social gaming mechanics that Zynga and its competitors have come up with this year.

So today, we’ll limit our comments on gameplay to noting that the game is extremely well-designed. Zynga’s evolution in sim games is clearly visible through FarmVille, FrontierVille and now CityVille, with a wider range of things to do and social features in each iteration. CityVille looks better, and is more fun to play, than its predecessors — even if the theme isn’t as interesting as FrontierVille.

Playing CityVille freely does seem to confirm some theories we initially had about the game. With full 3D graphics, CityVille steps away from the 2D pixel art that has defined most Facebook games.

We theorized before that CityVille is intended to translate to mobile devices, and indeed, during play the game actually seems like a mobile title — the art and animations feel more suited to an iPad than Facebook. CityVille also very noticeably lacks a player avatar of any kind. This may have been an intentional choice with mobile in mind, as avatars can be more difficult to use on a small screen.

Another idea we put forward is that CityVille is intended to begin siphoning players away from FarmVille; the latter game has aged, and no longer compares favorably to many newer titles. True enough, one of the first messages to pop up in the game asks you to recruit FarmVille-playing friends:

There’s also plenty of content that would make FarmVille players feel at home. Besides actual farm buildings and crops on a timed growing cycle, this quest about a poor, lost bunny should be familiar:

The last thing to note about CityVille is that it’s no alpha or beta launch. Although there are a few “coming soon” features like Wonders, the game looks fully built out, with features that most developers would have pushed off until a later update. Just to give one example of what we mean, there are already 119 different structures that can be built in the game.

CityVille will be the Zynga game to watch for the rest of this year. Zynga is busy overseas, but those efforts will take some time to mature. In the meantime, with Zynga’s advertising dollars and cross-promotional might, CityVille could well balloon into the tens of millions of players.