The Bourne Identity. Not great, but a very good genre piece. As many reviews noted, Matt Damon does lack the gravitas of, say, Richard Chamberlain, but he does a convincing enough job as a CIA hitman. The movie contains some fresh sequences -- the first car chase (involving a beat-up Austin Mini and some motorcycles), for instance, is unconventional, as is a climactic moment near the end of the film (a new take on the staircase shoot-out). Since it's so rare to see something you've never seen before in action movies, these moments make the movie easy to appreciate.
The acting (Chris Cooper, Brian Cox) believable and tense, even if the dialogue and plot don't make a great deal of sense. The one actor who seems out of sync with the rest of the movie is Julia Stiles, who is sort of stiff and always looks like she woke up late and is trying to convince everyone on the set that she isn't tired. She didn't have much to do, anway, so it's a minor quibble. Lola is good as the civilian love interest, and there aren't any dumb scenes where she knocks the bad guy over the head with a vase. Her confused, occasionally puppy-ish personality makes it a little hard to understand why Matt is so attracted to her, but she's nice enough. I guess he recently got exposed to his own human side again (this is implied in the movie), and so maybe that carried over into his relationship with Lola, or maybe he was getting in touch with his true self for the first time since his super-spy training began.
Before seeing the movie, I read 139 pages of the book. Let me tell you: don't bother. It is horribly written and seems to have almost nothing in common with the movie, besides the "secret agent has amnesia" premise, and of course, the title. Geez, and Robert Ludlum is such a big deal author and everything. It made me want to write a spy novel and become a best-selling author by the weekend.