What's the worst movie with the best trailer?

Movie trailers are an artform all their own. Sometimes the best part of sitting in the theater is watching five or six blow-your-hair-back fantastic trailers in a row. But they can be deceptive, too. What's the worst movie you've ever seen, that had the most brilliant trailer?

Please include the trailer in question — or else, maybe a representative picture or movie poster. And please mention the movie's title, and why it didn't live up to the terrific trailer. Thanks!

Top image: Terminator Salvation.