The only response that a very hasty search yields is in fact from Brian’s American Years, page 491:
“He [VN] also read and enjoyed Anthony Burgess’s Malay trilogy and began to read Saul Bellow’s Herzog, but found himself too bored to continue.”
Of course, we all know these are not black-and-white matters. There were many cases where VN’s assessments varied with periods and individual works (e.g. Dostoyevski, Pasternak et many al).
By the way, I have just approved page proofs of Englished "EASTER RAIN" for publication in CONJUNCTIONS and inclusions in next edition of COLLECTED
Best greetings,
DN