Earth is invaded by Martians with unbeatable weapons and a cruel sense of humor.
Fairly enjoyable sci-fi spoof works only to a degree, since it's thoroughly tongue-in-cheek, so that, ironically, the more straight-faced Indepedence Day from the same year was actually more fun.
Halliwell*: "The film begins brilliantly, with a stampede of flaming cows, but then is content to recycle, at great expense, the style of 50s sci-fi films while its cast parody their more serious roles; despite its occasional antic charm, it is not as enjoyable as it ought to be."
Maltin**1/2: "Overly self-satisfied spoof of '50s alien-invasion movies (and '50s attitudes)...Great effects and animation (of the Martian characters) but awfully broad and one-note in tone, spoofing something that's already funny in the straight-faced originals of the period. One can't completely dislike a film in which Slim Whitman figures so prominently, however."