Rats do not make good movies
Because Willard feels tormented both at work and at home, he is often a cowering fool. That is, until he discovers that he can control rats. He befriends a white one he calls Socrates, and finds solace with his new friends. As he realizes he can exert more power, he begins to become more ambitious in what he plans to do with his rats. The only rat he is wary of is a huge black one he calls Ben. He feels that Ben is jealous of his friendship with Socrates. Watching Glover tenderly talk to and pet Socrates is truly one of the more bizarre scenes in recent film. And his friendship with these rats is the catalyst he needs to come out of his shell. It gives him confidence, which soon turns to arrogance. There's also a pretty pointless role for Laura Elena Harring (John Q., Mulholland Dr.), who plays a co-worker who is the only person to reach out to Willard as a friend.
To say that Willard becomes homicidal does not give anything away. Director Glen Morgan, who also adapted the retelling, knows that this partially a horror movie, so it goes in that awkward direction. Most of the rats are computer-generated, and the film does a very good job on them. Morgan keeps the lights low (probably from his experiences on The X-Files) and gives everything a run-down, grimy look. It's also hard to tell exactly when Willard takes place. There is nothing specific to nail down a time; it could be now, or it could be twenty years ago. All this is to establish mood, and it does an effective job of giving Willard a creepy feel to it, like something is not right. Willard is not a great movie, and is probably not even a good one, but it is different enough to merit watching, especially for Glover.