His main contribution was making biologist consider that population size affects how fast selection changes a population, but he tended to imply this was some form of categorical difference and not a spectrum. But this was greatly overblown my media into some sort of insistence that they could not be the same. large population slow change and small population fast change are both points on the same spectrum. Nobody was right becasue both sides were not really saying the other could not occur they just emphasised their own area. Gould main problem was the idea of stasis in punctuated equilibrium that large populations somehow did not keep evolving this was a point he contested without ever really being able to provide evidence for. His own evidence often fit both interpretations. Since then it has been pretty thoroughly refuted by genetic studies, better resolution*, and modeling of stabilizing selection, all populations change, large ones just change slower, often with less direction. Gould himself later accepted this, but insisted on keeping the terms punctuated equilibrium and more oddly "stasis" for these periods of reduced change, this led to more misunderstanding especially with the public and media. Many scientist felt it was a sign of being unwilling to truly accept the evidence.
He also contributed a lot to our understanding of evolutionary development and how evolutionary baggage effects future adaptations. We often forget this but without his constant pushed of the importance of constraints and development both would probably be much more poorly understood. Panadaptationism was probably given more service by than many ever though it deserved, but Gould was right that that are far more aspects to selection than many considered. It just was not as popular an idea as his attention implied, but that is part of science harping on bad ideas is not really bad in science, it just starts to get old when the idea never had a lot of traction. It is however understandable considering Gould's own focus.
He has a serious problem(probably not unfounded) with sociobiology but probably pushed too far by implying searching evolutionary history for influence of our behavior was pointless. As much good as he did for understanding physical adaptations he seemed to have a blind spot when it came to behavioral adaptations. He mellowed about this in later years but still seemed to resist it. Sociobiology tended to be over applied, often without evidence, it was easily the worst offender with panadaptationism. Gould was right to push back against speculation but he often treated all behavioral science the same regardless of rigor.
Dennit who primarily researched evolutionary aspects of human behavior and publicly speculated a lot, of course ended up as a stanch opponent. But then as the more rigorous evolutionary psychology arose from sociobiology Gould seemed unable to see the difference which quickly led other to stand against him and probably did more than anything to produce his negative image. I know it is the thing that put me off his writing.
The other issue that I, as well as many other paleontologists, had with him was his resistance to the application cladistics and other computer based analysis. Both extremely important tools in understanding evolution, especially once to could be applied to genetic material. He always seemed to treat it as not real science, which always struck me as weird considering how much he emphasised rigorous investigation. He struck me a brilliant mind falling behind the technological curve and becoming disapproving of it. To myself as a young scientist he seemed to resist anything new regardless of rigor despite his own emphasis on rigor.
In short he was hard working scientist. He improved our knowledge in some areas while being unhelpful in others. He was a scientist who got a huge amount of media attention, which few scientist can do without sooner or later showing normal human flaws. Now take all this with a grain of salt, this is all my own personal impressions from observation of his work in paleontology along with reading his (and just about every other) book about evolution. I have not read many of his paper outside of paleontology. I say this becasue speculating on the beliefs and motivations of the dead has always struck me as dishonest especially without laying your cards on the table.
- I wanted to give special mention to resolution and darwin finches, darwin finches undergo different selection every year depending on rainfall, large and small (specialized) beaks during wet years and medium (generalist) beaks during dry years, this changes every breading season with the amount of rainfall on any large scale this would appear to be no change as they tend ot average out, but with better resolution we can see many many small directional selection pressures adding up to no net change on a large scale.