BOSTON — THIS past weekend the Loews Charles Theatre, with the help of the Boston Star Trek Association (BSTA), became Starbase Charles as the time-worn cast of the original Star Trek took to the screen for the sixth and possibly final time.Members of the BSTA, as well as many fans, came dressed in character, and before the show moviegoers could have their pictures taken in Klingon or Starfleet costume on a mock bridge in the lobby for a $5 fee. Proceeds were donated to charity. Walter Keoing, who plays Mr. Chekhov, welcomed viewers opening night. He gave away no secrets, but jokingly left the audience with the comment that "if every Star Trek fan sees this movie five times, maybe we'll be back." While the critics complain that the movie lacks originality and freshness of character, it does possess the two most important elements: it's entertaining and the audiences like it. Star Trek VI marries classic Trek characters with modern special effects. The characters return here with the same wit, humor, and distinctness of character for which they became known 25 years ago. But there's nothing new in their performances, and the movie is like watching a 90 minute series episode without the commercial interruptions. The good guys rate cheers; the villains are hissed; and everyone laughs at all the jokes, no matter how old and corny they are. The movie is simple entertainment: that's all. The audience participation makes the film worth seeing. When asked what "Star Trek VI" and the series in general has meant to her, Carol Jean Zelman, a 25-year fan and president of the BSTA, said "hope for the future."