John Carpenter had a fairly interesting idea for his film They Live, which transcends the horror genre the director usually works in. The concept, which is pretty obvious after 15 minutes, is that alien ghouls are using TV signals to mask their horrible appearance and the subliminal messages they use to control the consumerist society. If this were a sci-fi short story, it would be about 15 pages long. The problem is that Carpenter has stretched out a short story idea in to a novel-length movie, without adding to many other ideas. There is a famously long fistfight scene which is intentionally ridiculous and entertaining and ads about 8 minutes to the running time, though.