The great Terry Teachout addresses literary biographies:
Far too many new biographies—including a forthcoming book about a famous filmmaker that I read last week and will be reviewing later this year—are rigidly and reductively thesis-driven, an approach that never fails to remind me of what Earl Long, Huey’s brother, said about Henry Luce, the founder of Time and Life: “Mr. Luce is like a man that owns a shoestore and buys all the shoes to fit himself. Then he expects other people to buy them.” I loathe biographers who nudge you in the ribs every few pages, sticking in pointed little reminders that the deeply suppressed sadomasochistic tendencies (or whatever) of Flannery O’Connor (or whoever) permeated her life and thought and insinuated their way into every page she wrote, blah blah blah.
Also, note his list of “first-rate” biographies, none of which he wrote himself.