Despite the cheesy special effects and some unnecessarily silly scenes that greatly detract from the movie, 12 Monkeys is a very good science fiction movie.
Set in the year 2035, a plague has wiped out much of the human race and they are forced to live deep underground. Scientists of the era send criminals back in time, using imperfect time machine technology, to try to discover the origins of the virus so they can bring a sample back to the future to find a cure, and take back the planet. Bruce Willis plays Cole, who is sent back to find out who the 12 Monkeys are, which are believed to be a terrorist group responsible for the unleashing the virus. Unfortunately, he sent back to wrong time and finds himself in a mental institution. While there he is treated by a psychiatrist played by Madeline Stowe and runs into Brad Pitt - a wacky mental patient. It's hard to tell much more about the plot without giving the movie away, but these two characters play a vital role in the plot.
The director does an excellent job with the time travel elements of the story, an aspect that become quickly inconsistent and ruinous to a movie of this nature without careful attention to detail. The acting is also superb. I would highly recommend the movie.
Also note, the "Making Of" feature on the DVD is one of the few that I actually enjoyed and found quite interesting.