The IPCC is meant to assess the academic literature on climate change and policy so as to inform decision makers. This is important. It has also proven to be difficult to keep policy advocacy out of the IPCC.
There are two further issues. Some of the authors seem to have built a career on their involvement in the IPCC rather than on the strength of their research. This is just wrong. The IPCC should use the best people available, rather than the best IPCC people.
In some areas, the IPCC has deemed the available research to be insufficient and stepped in to develop the field. Scenario development is the prime example. Filling research gaps is always good, but in this case it led to the IPCC assessing its own work. The unsurprising result is that the IPCC declared that its own research is wonderful. I disagree, as documented here and here.
Now, there is a new development: The IPCC has started a scholarschip programme, seed-funded with the Nobel Peace Prize money. There is nothing wrong with that, of course, although one should wonder whether it is appropriate to lure bright young things in developing countries into climate research as that implies that they will not investigate other problems that may be more urgent. For the IPCC, there is the danger that the IPCC scholars of today will be preferred IPCC authors of tomorrow; and that their publications will be given preferential treatment in future IPCC assessments.