From Randall Jarrell's essays on Auden

Another of Auden's virtues is his great capacity for growth or change--he is as incapable as a chameleon of keeping the same surface for any great length of time. It is rather queer and pathetic to mention as a virtue this capacity for change, in the case of a man who changed away from his best poetry, got steadily worse, for many years, but he has begun to get better again, and is not laid away in that real graveyard of poets, My Own Style, going on like a repeating decimal until the day someone drives a stake through his heart.

Quoted by Charles Rosen in NYRB, Nov 20 08