A couple of clever turns don't rescue THE WATCHER from its tired plot, laughable dialogue, and disastrous casting. In other words, Griffin is the kind of serial killer who only exists in movies, more a plot device than a character. Any characteristic he has or is described as having is jettisoned without explanation when necessary for the purposes of the plot. Reeves can be effective in many kinds of roles, and can convey a spookiness that plays as shyness in one part or nihilism in another. But he fails to convey any sense of menace or evil. The movie would have been much more effective if Reeves and Spader had switched parts, with Reeves the damaged cop and Spader the obsessive killer. Tomei is onscreen long enough to show us how much more she can do. It is obvious from the beginning that her character is there to give Campbell -- and the audience -- a potential victim to care about. But she manages to convey such warmth, compassion, and charm, that despite ourselves, we do care about her.
The movie tries to show us that the cop and the killer have a lot in common. Both watch their prey, keeping track of every detail. Both seek an appreciative audience. Each fascinates the other. But the last half hour becomes ludicrous as Campbell engages in Stupid Movie Behavior #1 (things people do in movies that make absolutely no sense whatsoever but if the characters did what any intelligent person would do there would be no plot): after working closely with the local police every step of the way, Campbell goes to meet with Griffin alone, without telling anyone where he is. Then, when they do get together, the dialogue becomes so idiotic (Griffin tells Campbell that he gives Campbell's life meaning, and Campbell responds, "Do you know how many serial killers there are in Chicago? Eight!") that the movie loses any tension that it had.