Above all, he had, like one of his heroes, Walker Evans, that special American combination of democratic sensibility and a kind of natural aristocratic bearing. He believed that the best pictures were unpretentious and open-minded, but he also believed that some people were simply, even objectively, much better at taking them than everyone else (though this included some amateurs, and even some anonymous photographers), and he was perfectly dismissive of anyone who didn't meet his standards.
He had his blind spots, or perhaps he simply had his moment. In the years just before Szarkowski retired, the best of photography underwent yet another deep change, becoming integrated into the broader concerns of art in general, influenced by conceptualism, performance, painting. It is only slightly overstating matters to say that there's really no such thing as photography anymore. It simply doesn't exist, except as one of many ways to make something that counts as art; and as a result, there's hardly any need for departments of contemporary photography in museums at all. Szarkowski had little sympathy for the artists who broke down those barriers. The pioneers of the '60s, like Dan Graham, John Baldessari, and Ed Ruscha, and their successors—Sherrie Levine, Richard Prince, and so on—did not believe in photography as a distinct medium requiring special skills, and, with the possible exception of Cindy Sherman, Szarkowski did not believe in them.
If nothing else, it was an unfortunate lapse, but a great curator, like a great critic, has a limited shelf life, and that's as it should be. Any aesthetic passion worth holding will eventually be superseded by history, though its effects may be felt forever. Szarkowski, as I say, had his moment—a very long moment, in fact, and more importantly, it was definitely his. He managed it far better than most curators could have, and photography owes him an inestimable debt.