Maybe Thurber's last years were not quite as bad as they seem on paper. Certainly his steady drumbeat of complaints in the letters seems fairly standard for a New Yorker writer of the period. Grumbling was the house style, and Ross saw to it that his people always had plenty to grumble about by paying shoe-pinching royalties and editing like one of his dreaded schoolmarms. Also he used to reject even his stars just often enough to maintain maximum jumpiness. Later, Thurber would talk about how well he and Ross had worked together, but I surmise that this was mainly because he'd been riding so high at the time and was awfully easy to be nice to. It would be Ross' successor, William Shawn, who would inherit the delicate task of taking Thurber down a peg or two without bruising his self-importance.
Theoretically at least, The New Yorker still needed him, because his name still sold magazines. But he didn't need it. He began to write more and more books and pieces for less fussy magazines—pieces in particular on the state of American humor, about which he had practically nothing to say except, in effect, "I'm unhappy." Talent can retrace its steps and tell you how it got there. Genius is just there or it isn't.
Nevertheless, for 10 great years, he had had an extraordinary gift by the tail, and the whole world knew it, and who's to say it wasn't worth it? And one pleasant surprise that the letters suggest is that the gift itself never quite died. It turns up occasionally in the last letters as good as new. Since Thurber seems to have written letters the way kids today make phone calls, Harrison Kinney has, I think wisely, carved out just a few categories, so that while whole bits of Thurber may be missing, we do get complete pictures of his relations to colleagues and kinfolk and at last some sense of his second life in Bermuda. (I'll pass over Thurber's love letters here with just two glancing points.) We also get samples of his care and his courtesy to strangers he corresponded with, one of whom would turn out to be Peter DeVries, later his great protégé and probably the truest friend he ever had.
So, I don't feel a fan's protective urge to warn you off the letters. In fact, I myself found that I liked him very much on some pages and couldn't stand him on others. In other words, it was like meeting a real person, who is getting through his own particular hell any way he can.