Fortunately, there's enough in story mode to keep you and three friends entertained for quite some time. And there's plenty to do before or after you complete the actual plot. Even though Crackdown 2 feels more like Crackdown 1.5 than a true sequel, there is enough here and enough that has been improved that you will enjoy it just as much as the original, if not even more.
And there's always the hope (if not a certainty) that more will be added later via DLC, much like with the first one. But for now, wash your hands five times, make sure the stove is still off, check all the locks in the house three times, and get to some orb collecting.