It feels quite naturalistic to me in terms of dialogue and character reactions. The alien is obviously not realistic, but everything surrounding it felt like a very realistic response to such a fantastic situation.
Totally agree. Among the many
things that make The Thing so great - the acting, the music, practical effects, everything - at its core it's a simple, pretty universal tale and one we can all relate to, and easily works outside of its science fiction context (and has been, like in The Hateful Eight). Part of its brilliance is it's so easy to imagine yourself being there and how you'd react.
I always found the way the paranoia slowly ramps up to be all too believable and pretty chilling, especially because nobody in the movie is either an idiot or actively malicious (I'd argue even the Thing itself).
The book describes the form that it had when it was found in the ice pretty clearly, but it never reveals whether this was its true form or simply a mimic of the race that built the ship.
Always loved that particular bit. As a concept it's been used in a few other stories (probably all of which were inspired by Campbell's story).
It just makes sense and it makes the Thing (the creature) even more bizarre and mysterious.