They Live is one of those horror movies with something besides horror on its mind. It isn't so much that the Earth is being infiltrated by a grotesque alien race that can look like us, it is that they are using advertising and television to brainwash us. Years before Shepherd Fairey made his Andre the Giant "Obey" tags, this movie gave us a world where almost every piece of advertising or art doubled as a subliminal opiate for the masses.
Our hero, as played by "Rowdy" Roddy Piper of the WWF, stumbles across a box of magic sunglasses that allow the wearer to see through all the artifice of the world and determine who is an alien and who isn't. After a comically long "getting to know you" fight scene with Keith David, the two badasses decide to go on an alien killing rampage.
John Carpenter (of Halloween fame) takes all the ambiguity out of the situation. This most assuredly isn't a movie about a crazy guy shooting random people that he thinks are aliens. Although I think that could be an interesting movie. This has lots of fun action and 80s cheese in it. I think this movie will best be known for the line "I'm here to kick ass and chew gum, and I'm all outta gum." Silly fun.