"Downsizing" has generated jumbo-sized buzz at the Venice Film Festival. Viewers are debating how to describe it. Is it a science fiction film, a romantic comedy, a political parable, an apocalyptic thriller? Alexander Payne's movie mixes all those elements in its story of a man who tries to solve his problems by shrinking himself. That man is played by Matt Damon. Damon and co-stars Kristen Wiig and Hong Chau joined Payne on the red carpet for the film's Venice premiere Wednesday.