Susan (voiced by Reese Witherspoon) is a young woman from Modesto, California, who is set marry Derek (Paul Rudd), a TV weatherman who dreams of becoming an anchor on a big television network. She is outside in a field when a meteor crashes, and she is infected by its residue. The result: she turns into a 49 feet 11 inches tall woman. General W. R. Monger (Kiefer Sutherland) has her taken away to a top-secret prison where other "monsters" are incarcerated. There Susan, who is renamed Ginormica, meets Dr. Cockroach (Hugh Laurie), a gifted scientist with the head of bug; Missing Link (Will Arnett), a fish-ape hybrid; Bicarbonate Ostylezene Benzoate, or B.O.B. (Seth Rogen), a blue blob that gobbles everything up; and Insectosaurus, who at 350 feet towers over Ginormica.
When an ominous robot lands on earth, the President (Stephen Colbert) tries to communicate with the alien with music in a very funny take on Close Encounters of the Third Kind. It doesn't work and neither does all the military's firepower. General Monger decides to call upon the Monsters in hopes that they can defeat the gigantic robot. A confrontation takes place on San Francisco's Golden Gate Bridge.
Monsters vs Aliens is a 3D animated feature film for the family. Directors Rob Letterman and Conrad Vernon reveal their affection for "B" movies from the 50s as well as Mad Magazine of the period. The most appealing quality of the story is Susan's transformation from an ordinary woman who is living through her fiancé into an extraordinary superhero as Ginormica. She comes into her own in the last segment of the story when she takes on Galaxhar (Rainn Wilson) who has a plan to take over the earth with his army of clones. If you like rooting for the underdogs, you will find yourself cheering for Ginormica and her outsider companions.