Crap film
I think some films just don't age well, not just effects but the stories too. I am sure I would have liked this more if I saw it in the 80s, especially if I was a kid, but watching it now I just think it is bad.
There are large parts of the story I like, the creature on the loose thing is good, it is an exciting idea and works well for horror. Also the 'which one is still human' thing is cool, reminded me of Agatha Christie. But I just don't think this film does either of those things well and lots of films do both of those things better. There also isn't much left for this film, the action isn't interesting or exiting, none of the characters were developed enough that I cared about any of them, the Thing itself I didn't find scary or creepy and it wasn't shown well enough, etc.. Just bad overall.
I am assuming this was based on a book, and I am assuming as usual the book is great and the film sucks in comparison. But this gets >8/10 so I was expecting more.
Mostly it reminded me of an old X Files episode that was clearly inspired by this, but which I enjoyed more than this film. And also other films like Alien and Predator which I think are much better than this.