The above review of this book does a great job already, so I will try to complement it as best I can. Deleuze is a difficult thinker for newcomers. His ideas tend to refer to one another and have developed into a complex network of concepts over the course of his writings. The good news is that Deleuze is drawing an immense amount of interest in the US and UK now.
Deleuze sets out in the cinema books to create a theory of film and the image that stands in sharp contrast to the film theory we're most accustomed to. Deleuze does not accept that narrativity is a given in film. In fact, he wants to find a way of appreciating and describing what distinguishes film from language and narrative systems. For Deleuze, the moving image is not a system of reference. One doesn't refer to something through a segment of film. The filmic medium is direct, not referential.
Cinema 1 is thus a look at how the early cinema learned to produce the "movement image." It's a review of "auteur" film-makers and their experiments with the medium (in addition to those mentioned above are Welles, Godard, Eisenstein, Lang, Resnais, Hitchock...) to produce perception, affect, and action.
He contrasts montage with mise-en-scene. He shows how action corresponds to situations, either responding to situations or modifying them. He describes the discovery of depth of field, and use of affect in close ups and still images, the importance of shot and reverse shot sequences, and movement within the scene vs of the camera. He shows how pre-war film maintained a commitment to the whole. Characters' actions were motivated by situations, and films as a whole hung together.
The book concludes with Hitchcock's invention of the audience as a third term in the filmic experience: subject, object, audience. Audiences complete Peirce's sign system (firstness, secondness, thirdness) because they interpret the film. Indeed, Hitchcock's art was in showing the audience what the character would only discover later, and in making his films into logical puzzles rather than whodunits.
A dazzling book, I had to read it twice, and many of the films referenced won't be on dvd for years....