It was released worldwide in November 2010 for Microsoft Windows, the PlayStation 3, Wii, and Xbox 360, with a separate version for Nintendo DS developed by n-Space. Aspyr later ported the game to OS X in September 2012. It is the seventh title in the Call of Duty series and the sequel to Call of Duty: World at War.
Yes, the majority of the Call of Duty games are set within the same universe, with interconnected storylines and recurring characters. However, some of the games, particularly those in the "Black Ops" and "Modern Warfare" sub-series, have their own separate continuities and story arcs.