I read the book first, though. And here's the quandary. When I read the book first, I know too much. I do not know how the film seems to those who have not read the story ahead. I suspect that in this case the quick cutting, the rapidfire shifts in scenes, would have to be confusing to others. Although the story is necessarily simplified - the book is large and complex - still there are many characters and the thread might have been difficult to follow.
Given that, I can still recommend the film. For two reasons: the casting and the African scenes. The film added to the book in this way, in making concrete the landscape, the African people, which are sketched rather lightly in the book. And the two primary characters are well-cast: Ralph Fiennes and Rachel Weisz (sp?). I don't think I have liked Fiennes as well in any other film. In this one he is entirely likeable, although his transformation from a "constant gardener" to a person obsessed with finishing what his murdered wife started, at much cost to himself, is not so easily followed. Rachel is, thank heaven, not a cutesy heroine, not an unbelievable beauty simplistically obsessed with justice. She broadcasts intelligence, even when given some lines that (again, to simplify the plot) are hardly memorable. And she doesn't do those irritating "feminine" things like chewing her lip or flipping her hair. She really seems a beauty who is not conscious of her looks.
I believe that the screenwriter did a decent job in cutting the story to the bone and fleshing it out somewhat differently than the original, even considering one of the final scenes, in which more justice is actually achieved than is so in the book. John LeCarre, to his forever credit, is gutsy enough to portray the truth in his books, even when that means characters are flawed and driven by less than noble desires. Even when that means that his country - Great Britain - does not come across as particularly honorable. Even when the ending is depressingly dark. Which is not to say that this story is wholly believable, of course. The background is more real than some people probably realize, but the individuals, the main characters, are larger than life. And yet....there are no superhuman feats. It seems a story that could have happened.
Terrific book. Decent film.