It's a quite a different movie — though the "plot" of La Jetée remains more or less intact, it's more of a framework on which other plot threads are hung, or warped around. It is resoundingly a Terry Gilliam film; Brad Pitt and Bruce Willis both give remarkable performances as the mentally disturbed antagonist and protagonist, respectively — you can see why they wanted to be in the movie, because both cut hard against their popular personas.