I can't believe that this film was a failure on its release as it is one of the true classics of the genre. Critics and the public found the body horror of the film too nauseating but Rob Bottin's truly 'out of this world' creations remain a highlight in the world of special effects, and like American Werewolf, all the more effective for being real, practical SFX rather than CGI (which is what would be used in the much-mooted prequel I'm sure). So Palmer's response to seeing a head sprout legs and scuttle away is exactly the same as the audiences "you've gotta be fucking kidding".
I have done film courses on the horror genre before and in them I have talked about the differences between tension and suspense. Suspense is where the audience knows more than the characters. For example, when the audience knows the killer is in the house and is waiting for them to jump out on their victims. Tension however is where the audience know as much as the characters, and this is what makes The Thing so effective.
You have a large group of people in an isolated location who are infiltrated by a shape shifting alien. They know that (at least) one of them is The Thing, and so do we, but nobody knows who it is.
This leads up to one of the best scenes in the movie and in cinema as an example of tension, the blood test.
Also contains one of cinema's best tag lines (Man is the warmest place to hide) and last lines, when two characters (no spoilers) sit down in the frozen camp and suspicious of each other, share a drink "Maybe we'll sit here a while, see what happens".