As The Bourne Identity's on-the-run amnesiac hero, Matt Damon, playing an assassin without a cause, gets to show off some deftly timed martial-arts moves, flipping his limbs around with the slashy precision of ninja nunchakus. Damon's character, Jason Bourne, is some sort of black-ops shadow agent on assignment in Europe; after getting injured in a mysterious fracas, he has lost touch with any memory of who he is or how he got there. The movie has a few whispers of intrigue, but at its heart lies a dispiriting paradox: The more that Jason Bourne learns about himself, the less arresting he seems. ''The Bourne Identity'' plays like John Le Carre with a couple of burned-out cylinders. The film wants us to look at these CIA superkillers and say, How ominous. Instead, a lot of viewers may now think, As if, or even If only.