John Carpenter's 1988 film, They Live, is about a lot of things.
Primarily, it's about a homeless man who finds a pair of sunglasses which allow him to see the alien invaders who are taking over the Earth. Using these sunglasses, he joins a resistance force trying to reclaim Earth from its alien conquerors. And he does so in the manner he know bests. Namely "kicking ass and chewing bubble gum"! And he's all out of gum (yes, this is the movie that line comes from).
On it's most basic level, They Live is a generic sci-fi action film starring a professional wrestler (Rowdy Roddy Piper) in the lead role. But just under the surface is a sly social commentary. In They Live, the aliens conquering the world have disguised themselves as human beings. Using their disguises, these aliens have occupied positions of wealth and power. Their tools of domination are mass-media broadcasts influencing the general public to watch TV, consume commercial products, and stay in dead-end jobs. The aliens are deliberately breeding economic strife to turn humanity against itself with poverty and deprivation.
In short, the aliens are the Republican party under Reaganomics.
Carpenter is pretty obvious in his critique of 80s commercialism and the domination of the American rich. But what this leaves the viewer is a ridiculous action film with just enough social relevance to give you an excuse for enjoying it. It's true that the ridiculously long (and infamous) back alley fight scene between Roddy Piper and Keith David is reason enough to watch the movie. But the social commentary, goofy plot, and well crafted direction make this movie essential cult sci-fi viewing.