I typically find myself having difficulty with comedies, but this film manages to succeed thanks to a strong cast, well-written jokes that move at a good speed, and some appealing visual effects from Stan Winston. It’s full of playful jabs at science fiction – especially "Star Trek" – presented in a way that feels both understanding and enjoyable. The characters portraying the “crew” are former performers making appearances at comic conventions, with Tim Allen as the arrogant Captain, Alan Rickman as a wonderfully distant actor playing the disheartened, partially crustacean ship’s doctor, Sigourney Weaver as the curvaceous but ultimately unnecessary "Tawny Madison," and Tony Shalhoub as the engineer aboard the “NSEA Protector.” During one of these events, they meet the "Thermians," who require assistance in confronting the malevolent, all-powerful "Sarris." Having observed broadcasts of "Galaxy Quest" and mistaken them for authentic historical records, the "Thermians" have constructed a genuine starship and are counting on the crew to embody their characters as closely as they did in their scripts and rescue everyone. Everyone delivers a good performance; even Sam Rockwell is memorable in the familiar Trekkie “red shirt” role (anticipating imminent demise). It might not elicit constant laughter, but if you appreciate this kind of movie, you’re sure to smile often at the humorously presented fight sequences; naturally, the captain's shirt gets torn – and each character discovers a small measure of bravery within themselves. I really enjoyed it!

Source on TMDB