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 and 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.
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.
At least to U.S. astronaut Captain Charles T. Baker who lands on Lema’s planet hoping for a quick flag plant and a hasty return to earth and his millions of screaming fans.
But on this alien planet the media has tagged spacemen as brain-eating, zombie-creating monsters, causing Baker to run for his life and into Lema’s house.
Now it’s up to the green native to get the clumsy astronaut back to his spaceship before military dictator General Grawl and mad scientist Professor Kipple manage to exterminate the Earthly visitor.
enjoy! 
magic