Jackie Gavagan, whose husband, Donald, worked in the World Trade Center and died in the Sept. 11 attacks, went to the movies a few weeks ago for a brief escape from her hectic life as a widowed mother of three. But as the trailer for United 93 began playing, images of the burning Twin Towers gave Gavagan an all too heavy dose of reality. "It really disturbed me," she says. "I've never cried at a movie before, but there I was, sobbing at a preview."

The first feature film to dramatize the events of 9/11, United 93—which depicts how passengers fought back against hijackers on the flight that crashed in Pennsylvania—is slated to open April 28 but has already stirred controversy. Complaints from moviegoers prompted a New York City theater to stop showing the preview (studio Universal Pictures created a behind-the-scenes featurette theaters can show instead). United 93 producer Lloyd Levin says he is "sorry" the trailer distressed some viewers: "The hopes were to provoke discussion."

And the movie itself? Several family members of Flight 93's 40 passengers and crew expressed strong support in interviews with PEOPLE. "It was extremely hard to watch, but I think very, very important," says Sandy Dahl, widow of pilot Jason Dahl. "We must never forget [their] bravery." Directed by Paul Greengrass ([The Bourne Supremacy]), the film cuts between events on the plane, air-traffic control towers and military commands, mixing improvised dialogue with lines based on recordings made on Sept. 11.

With the Oliver Stone-directed drama World Trade Center due out in August, the response to United 93 will test whether America is ready for Hollywood's take on 9/11. "I'm proud of [United 93] and the message it sends that ordinary people can do courageous things," says Paula Nacke Jacobs, whose brother Louis died on the flight. "When I hear people say it's too soon, it can never be soon enough."