I don't know if plodding storylines and two-dimensional characters is fair, some of his novels spend a lot of time watching characters do science (like the orthogonal triology) so it can get slow but he's still banged out plenty of great plots and action setpieces and characters that develop. The second book of Orthoganol has some amazing action set pieces (solidly based on the weird rules of an imaginary universe) and plot developments. General consensus is that his short stories are the best.