David X. Noval in The Critical Flame:
Claude McKay, born in Jamaica in 1890, is the first modern master of the sonnet form. Yeats of course had turned out a few—one a classic—as had Pound. Cummings wrote plenty of sonnets, but, because of their idiosyncrasies, they are more complications than masterworks. Wilfred Owen, if he had lived, might have rivaled McKay, as he was disposed to the sonnet and masterful in its usage. The only other serious contender, to my mind, would be Edna St. Vincent Millay, and perhaps later, Berryman. In the Selected Poems, first published in 1953, several years after his death, Max Eastman writes (with what McKay’s biographer, Wayne Cooper, generously describes as an “unconscious condescension”):
Claude McKay was most widely known perhaps as a novelist, author of Home to Harlem, a national best-seller in 1928. But he will live in history as the first great lyric genius that his race produced.
Why then has McKay’s work languished in relative obscurity? Eastman writes in 1953 that his “place in the world’s literature is unique and is assured.” Yet in his fifties, after a decade of illness, McKay sought to end his financial difficulties by taking on employment as a riveter—something he was not physically equipped to handle, and which surely contributed to a stroke at age fifty-three. He had turned down a “sizeable” book advance, explaining, “I haven’t been able to concentrate on a plot. It’s quite impossible when one’s mind is distracted. People can’t realize the state of one’s mind under such conditions, and the few I meet make me angry by telling me how happy I look.”
More here.