Miramax pulled such a trick with The Crying Game to hype a film in America that did "ho hum" business in England.
"Don't give away the ending!" "What is the secret?" "Have you heard about the Crying Game?"
Well their job is to get as many people as possible to see the movie and mysteries like that are a good way to do it. I think it's almost impossible to convey what's good about a movie through trailers. They either make the film seem worse or better then it is.