Wonderful, wonderful, wonderful. I know I recommended another book of film reviews six weeks or so ago (Anne Billson's Spoilers), but this is different. For a start, it has got to be over half a million words long. The judgments about the films all come after much reflection, rather than to meet a deadline; and some of the films are very old indeed. We start, in time, with 1895's L'Arroseur Arrosé; alphabetically, which is how the book is ordered, we start with Abbott and Costello Meet Frankenstein, which I think is the book's one mistaken inclusion, although one salutes the perversity of the choice.

And of L'Arroseur ...? "A man is watering his lawn with a hose. Behind him, a joker, a trickster, the spirit of Peter Lorre, steps on the hose ... And somewhere way down the line - it may take over 50 years, a man with an empty nozzle (think of Javier Bardem in No Country for Old Men) is going to stumble towards us, pained, wronged, and driven by the pain to murder but asking us what it is we want of him."

In his introduction, Thomson regrets how "otherwise sensible people write PhD theses on particular movies without ever seeing them on a large screen". The result is that their writing "is a little dry, or a little short of what I recall as magical effects". Thomson's writing is the opposite of dry, and full of magical effects. "The spirit of Peter Lorre"!

There are very few films which you feel should be in here but are not - for all that Thomson says "how is it that a thousand seems to omit more than a whimsical ten?" But this is not only a book 100 times as useful (more, in fact) than a top-10 list; it also contains films he does not like, but which grabbed our attention once, or still do, for reasons which mystify him. Of The Sting: "There are no characters, no context, no time or place, and not the least gesture toward any other meaning. It leaves one thinking that Butch Cassidy and the Sundance Kid might have been written by Saul Bellow." Of The Sound of Music: it "has to be in the book, if only because millions of the stupid and aggrieved will write in to the publisher, 'Where was The Sound of Music?' if it is not. It is here." (The only film whose omission is genuinely regrettable, I think, is Powell and Pressburger's astonishing A Canterbury Tale - but then A Matter of Life and Death, The Red Shoes and Blimp are here, as is Powell's Peeping Tom ("a masterpiece full of dread ... cold, nasty and alienated and it knows how far those things are akin to the reptile machinery of film itself").

This is, in a way, the reverse of his monumental and ground-breaking Biographical Dictionary of Film. Although you might wonder, if you had no deep affection for the medium, what the point would be of such a book as this. A thousand is not inclusive enough to be useful for reference; and one can make up one's own mind, surely?

Well, no, sometimes one's own mind is not enough. It is one of the virtues of great criticism that it can not only articulate what you were feeling but couldn't quite phrase; it can alert you to things you hadn't picked up on in the first place. Thomson's criticism does both, and one of the reasons I managed to finish this in less than a week, or as near as dammit, is because every piece here, pithy and engaged, is like listening to an intelligence so deft and enraptured with its subject that it has become almost musical.

What Thomson does not know or feel about films is not worth knowing or feeling. His love of the medium is coupled with a passionate intelligence; entirely jargon-free, his prose penetrates to the heart of a movie even when you find yourself disagreeing with him. This is not often. And there are plenty of films here that you will not have seen, and that you will, after reading Thomson, very much want to. This is another job of the critic: to be a culture's guardian. He does it brilliantly.