The Thing (1982) by John Carpenter is a masterpiece of many crafts. The practical effects, especially for the time, are the best from any horror movie. All of the character designs are terrifying to the core. The dedication of Rob Bottin to his craft is amazing.

The way that any character can be hiding as the thing causes nearly every scene to be held with a strong tension that never releases. The decision to have the first human infected character represented as a shadow is a great way to establish that no character can be fully trusted.  The subtle hints that Carpenter gives take years and an attentive eye. The impressive effects that the movie has easily make it one of the best movies of all time.