Shinkiro has always been a great painter, from a technical standpoint he's truly a master. Fantastic use of colors. But of course most of his characters looked alike, and if I had to take a guess, I'd say that he probably heavily relied on photographic reference to compose his works. When you use real people for a comic/manga style, you'll get some problems and I see all the issues in his illustrations: a lack of dynamism, realistic/boring proportions of the bodies, an excess of detail (due to the temptation of preserving what's in the photo) and even cloned faces, if you're hiring the same model over and over. This happened even with great oil painters three or four hundred years ago, you'll see tons of replicated faces and even start recognizing the model (Shinkiro's model must've had a thin nose and a strong jaw).