Isaiah Berlin

Paul Johnson, writing a book review in The Spectator of "The Letters of Isaiah Berlin", asks "how serious was he?" He was not really a philosopher, Johnson says, and confessed he had never been able to understand Kant's "Critique of Pure Reason". I would like to know someone who does understand it. I tried to read it a long time ago and failed dismally on about the third page.
But I can't read Isaiah Berlin either. Which is strange because I always found him easy to follow whenever he appeared on TV explaining what philosophy was all about (usually with Brian Magee).
Talking about a subject off the cuff, so to speak, some people can do well but when they settle down to write a piece on the same subject they often founder. A professor of philosophy, who used to give extra mural lessons I went to, was a brilliant talker but when, one day, he read something from a book he was writing, he was incomprehensible. Maybe Isaiah Berling was like him: an easy talker who, when going to write something down, had a fear that other philosophers might take him apart, so used a style that was so perfect logically but which manifested itself as impenetrable.
Isaiah Berlin was a sort of unpaid ambassador to America in the early part of WW2. Winston Churchill, at a dinner with guests one evening was sitting next to Irving Berlin who, hearing his surname, mistook him for Isaiah Berlin.
"How's does Mr Roosevelt feel regarding the war in Europe?" he asked Irving Berlin who is supposed to have replied "Huh?"