John Carpenter's The Thing is currently my favorite horror movie. The inhabitants- scientists, pilots, etc.- of a research station in Antarctica are confronted by a terrible shape-shifting alien that takes the shape of people/animals it kills. Everything about the film is just perfect, but the main reason I love this film is rather simple. The characters in the film act like any person, with common sense, would act in this situation. They almost do everything that they should do and show great courage in the face of an enemy that could come from anywhere and be anyone. The casting is spot-on, with Kurt Russel providing Carpenter with another iconic performance as R.J. MacReady, the practical special effects still hold up, and the film is so complex that it will stand as one of the greats for years to come.
Check it out. I give it a 5/5.