The cast members of a tacky '80s sci fi TV show (somewhere between the '80s Buck Rogers and the original Star Trek series, in terms of both cheese factor and cult appeal) have found their careers floundering in the '90s, relying on embarrassing appearances at fan conventions just to pay the rent. Then a particularly odd collection of fans turns out to be actual aliens who have watched every episode of the show and believe it to be real - in fact, they have based their entire technology on stuff they watched on the show. Taking the TV "starship crew" for the genuine article, they whisk the show's befuddled cast members off into space to help them save their people from destruction.
Despite the high-concept setup, one which could have easily led into something corny and stupid, Galaxy Quest winds up being tremendous entertainment. It's not only very funny, it's also surprisingly smart about the sci fi genre (and its fans), with a formulaic but very satisfying story and a proudly skewed sense of humor. The cast is great, especially Tony Shalhoub's laid-back "science officer", Sam Rockwell as the paranoid cast member who fears he will be the first to die in their real-life adventures, since that what characters like him always did on the show, and Enrico Colantoni's hilarious head alien. The special effects are as impressive as they come. You aren't supposed to get anything out of this other than a good time, and on that, Galaxy Quest delivers.