Call of Duty titles have always nominally had a single-player campaign, and several of them have even been damn good campaigns. Modern Warfare the first immediately springs to mind as a damn fine single-player experience for the story, and Call of Duty 2 is also very good. I know people who swear by World at War/Black Ops, but I've always been of the opinion that Treyarch somehow manages to dick up everything good they manage to do the first time.
Call of Duty 3 is outright bad, from a game design standpoint. The lack of a sprint function is criminal in a game that included significantly more machine guns than any of the previous titles, and long, only half-obstructed view lines meant that your normal movement speed was "Please shoot me", and the story wasn't that riveting, either.
In World at War, (IMO, at least) it was how they deliberately set the tone as dark as possible, to the point of it sometimes being uncomfortable to play. The American part of the story might as well be "Do sadistic things to the Japanese, and watch your squad die slowly", while the Russian part of the story could be equally easily condensed to "Do sadistic things to the Nazis, and then do it even harder".
I can't actually admit that I've played the Black Ops campaign at any point, so I can't offer an honest opinion on it, but it feels like it fell prey to "New scenery syndrome" like Modern Warfare the second.
