Astronot Amerika, Kapten Charles “Chuck” Baker, mendarat di Planet 51 dan yakin bahwa ia adalah orang pertama yang mendarat disana. Ia terkejut karena planet tersebut dihuni oleh makhluk bertubuh kecil berwarna hijau yang hidup bahagia dan satu-satunya hal yang mereka takutkan adalah makhluk asing – seperti Chuck! Dengan bantuan robot bernama “Rover” dan teman barunya, Lem, Chuck harus menjelajah Planet 51 agar terhindar menjadi penghuni tetap Makhluk Penyerang di museum Luar Angkasa Planet 51
It's an "ET-in-reverse" story. An Earthling astronaut gets stuck on what he calls an alien planet. The local green folks call him (accurately) the alien. The story is a fond tribute to drive-in's, space-creatures sci-fi, and the 50's. With the Area 51 reference in its title, you know the film will be poking fun at everything it can get its hands on, including itself. It delivers this.
There's hover craft that look like big-finned autos of that era, black & white TV, and pioneer rock 'n' roll. It's clever humor, although some of this has been done before. There's a lot of parallels to Monsters vs. Aliens, too, in that frequent references to classic sci-fi flicks (up to the present, not just the 50's) pop up in sight gags and one-liner jokes. My fav was the character that resembled the Aliens movie creatures. There are other clichés sent up for satire: a loud mouth hawkish general, a wanna-be scientist, etc. Adults won't be bored thanks to these in-jokes, and the kids should like the slapstick stuff.
The film boasts a great idea, and some, but not all, of the potential is utilized. It's good natured and fun, rating about average for an animated feature.