Maybe my recollection of the book is wrong, but I thought that The Bourne Identity started out a lot like the book, and then just made up its own plot. Seems like a strange approach to the first of a trilogy of books: I guess they’re planning it as a one-off (although when does that really happen?).
Leaving its digression from the original aside, it’s quite a watchable action movie with a quite credible and strong female character (not your typical Arnie movie offsider). Matt Damon comes across as a really nice guy, trapped with the reflexes of a trained killer – the movie’s Bourne is not so far from the book’s in that regard.