There may be some Star Trek fans who find Galaxy Quest offensive. I hope not, because it seems to me to have been made with a considerable amount of affection for the source material. It makes fun of the ridiculous aspects of television science fiction and of fandom, but it also highlights the heroic intentions of Gene Roddenberry's original series.
The cast are so great it's difficult to pick out individual performances. Tim Allen does a fantastic turn as a washed up star who unleashes his inner Kirk. Sigourney Weaver gets to make knowing jokes about her hair, cleavage and those pesky air-ducts. Alan Rickman, Sam Rockwell, Tony Shaloub and Enrico Colantoni are all fantastic. The effects, story, bad guys and the jokes are all perfect. It's a comedy I can watch repeatedly. Great fun.