To oversimplify, the Julio-Claudians get the most attention; the five emperors after the Flavians the most praise. However, the Flavians, that oft-forgotten middle child, strike me as the most informative. If you understand the Flavians—their ideology, successes/failures, innovations/conservations, and the dynasty's narrative arc as a whole—you understand the first three centuries of the Roman Principate. I don't believe that this is true for any other set of emperors. In this, Levick's biography is crucial.