Assessment by peers
Damon Knight described Campbell as a "portly, bristled-haired blond man with a challenging stare." "Six-foot-one, with hawklike features, he presented a formidable appearance," said Sam Moskowitz. "He was a tall, large man with light hair, a beaky nose, a wide face with thin lips, and with a cigarette in a holder forever clamped between his teeth", wrote Asimov.
Algis Budrys wrote that "John W. Campbell was the greatest editor SF has seen or is likely to see, and is in fact one of the major editors in all English-language literature in the middle years of the twentieth century. All about you is the heritage of what he built".
Asimov said that Campbell was "talkative, opinionated, quicksilver-minded, overbearing. Talking to him meant listening to a monologue ..." Knight agreed: "Campbell's lecture-room manner was so unpleasant to me that I was unwilling to face it. Campbell talked a good deal more than he listened, and he liked to say outrageous things."
British novelist and critic Kingsley Amis dismissed Campbell brusquely: "I might just add as a sociological note that the editor of Astounding, himself a deviant figure of marked ferocity, seems to think he has invented a psi machine."
Several SF novelists have criticized Campbell as prejudiced - Samuel R. Delany for Campbell's rejection of a novel due to the black main character, and Joe Haldeman in the dedication of Forever Peace, for rejecting a novel due to a female soldier protagonist.
British SF novelist Michael Moorcock, as part of his Starship Stormtroopers editorial, said Campbell's Stories and its writers were "wild-eyed paternalists to a man, fierce anti-socialists" with "[stories] full of crew-cut wisecracking, cigar-chewing, competent guys (like Campbell's image of himself)", who had success because their "work reflected the deep-seated conservatism of the majority of their readers, who saw a Bolshevik menace in every union meeting". He viewed Campbell as turning the magazine into a vessel for right-wing politics, "by the early 1950s ... a crypto-fascist deeply philistine magazine pretending to intellectualism and offering idealistic kids an 'alternative' that was, of course, no alternative at all".
SF writer Alfred Bester, an editor of Holiday Magazine and a sophisticated Manhattanite, recounted at some length his "one demented meeting" with Campbell, a man he imagined from afar to be "a combination of Bertrand Russell and Ernest Rutherford." The first thing Campbell said to him was that Freud was dead, destroyed by the new discovery of Dianetics, which, he predicted, would win L. Ron Hubbard the Nobel Peace Prize. Campbell ordered the bemused Bester to "think back. Clear yourself. Remember! You can remember when your mother tried to abort you with a button hook. You've never stopped hating her for it." Bester commented: "It reinforced my private opinion that a majority of the science-fiction crowd, despite their brilliance, were missing their marbles."
Campbell died in 1971 at the age of 61 in Mountainside, New Jersey. At the time of his sudden death after 34 years at the helm of Analog, Campbell's quirky personality and eccentric editorial demands had alienated a number of his most illustrious writers to the point that they no longer submitted works to him. After 1950, Theodore Sturgeon only published one story in Astounding but dozens in other magazines.
Asimov remained grateful for Campbell's early friendship and support. He dedicated The Early Asimov (1972) to him, and concluded it by stating that "There is no way at all to express how much he meant to me and how much he did for me except, perhaps, to write this book evoking, once more, those days of a quarter century ago". His final word on Campbell, however, was that "in the last twenty years of his life, he was only a diminishing shadow of what he had once been." Even Heinlein, perhaps Campbell's most important discovery and a "fast friend", eventually tired of him.
Poul Anderson wrote that Campbell "had saved and regenerated science fiction", which had become "the product of hack pulpsters" when he took over Astounding. "By his editorial policies and the help and encouragement he gave his writers (always behind the scenes), he raised both the literary and the intellectual standard anew. Whatever progress has been made stems from that renaissance".