Prothero explains that the revelation was that species (at least as described by fossils) mostly don't change, but rather are in stasis for most of the time. Gradualism, as proposed by Darwin, doesn't describe the change of species very well.
For the first decade after the paper was published, it was the most controversial and hotly argued idea in all of paleontology. Soon the great debate among paleontologists boiled down to just a few central points, which Gould and Eldredge (1977) nicely summarized on the fifth anniversary of the paper’s release. The first major discovery was that stasis was much more prevalent in the fossil record than had been previously supposed. Many paleontologists came forward and pointed out that the geological literature was one vast monument to stasis, with relatively few cases where anyone had observed gradual evolution. If species didn’t appear suddenly in the fossil record and remain relatively unchanged, then biostratigraphy would never work—and yet almost two centuries of successful biostratigraphic correlations was evidence of just this kind of pattern. As Gould put it, it was the “dirty little secret” hidden in the paleontological closet. Most paleontologists were trained to focus on gradual evolution as the only pattern of interest, and ignored stasis as “not evolutionary change” and therefore uninteresting, to be overlooked or minimized. Once Eldredge and Gould had pointed out that stasis was equally important (“stasis is data” in Gould’s words), paleontologists all over the world saw that stasis was the general pattern, and that gradualism was rare—and that is still the consensus 40 years later.Stasis, which I have blogged about previously, is not nothing, but a phenomenon to be explained. Why would populations not change gradually, as some had expected? The environment does change ever so often, perhaps even what cold be termed gradually at times. Does stasis in the fossil record have to do with the fact that the information we get from fossils are predominantly about the morphology of vertebrate skeletons? Could it be that gradual changes in response to selection causes gradual changes in traits that don't affect skeletons (such as physiology or behavior)? Could there be general features of genetic architecture, for example, that constrains how skeletal morphology can change?
Alternatively, are is there evidence of stasis on other kinds of traits?
Gould, Shermer, and Prothero in 2001.