David Thomson has been an essential writer on film for around half a century, but in certain circles his reputation has long been in decline. The reasons are obvious enough. He writes too much, and sometimes carelessly; he lets his feelings run away with him; an Englishman who followed his dream to the United States, he hardly pretends that Iranian cinema, say, could possibly be as important to him as Hollywood. He has also developed a habit of launching sweeping attacks on the medium itself, which have the tang of personal bitterness, as if he regrets not dedicating his gifts to a more worthy muse.