The Thing is one of my all-time favourite movies. After watching it again recently, I spent hours inside IMDB's trivia and fact sections, and when one comment mentioned "the novel", I had to dig deeper. I then found not only that there is a novel about the movie, but the even more interesting fact that the novel is based on the movie script, but not on the movie itself. This means that there are a few differences between both, making the book a nice addition. After reading it, here are my thoughts.
First of all, the book contains way more dialogue and background details about the party members. In some cases would still feel like redundant information in the movie, but at times the dialogs provide better explanations, like why folks act as they do, or we learn that Macready is a Vietnam veteran (not just a badass pilot). I must say that the movie still was able to compress and distill the most relevant parts of the conversations, it is still quite comprehensible. Just not as detailed.
There are also a few scenes totally missing from the film and a few others that were shortened, especially during the second half of the book. The last chunk, without spoiling anything, is very similar in concept, but with a few notable changes in execution.
And of course, there are a noticeable amount of changes: While "the thing" in the movie is very shape-changing, the book tends to attempt to revert to its original form (or at least a preferred form), resulting in many of the scenes involving the creature playing differently. The expedition voices way more of their thinking on how they guess the monster thinks and acts, providing more context on why they later do other actions. MacReady's character feels a bit different too, maybe having too many angles inside a not-too-long book (around 200 pages).
Overall, the reading felt like a very curious experience, something very familiar and known, and yet new and different. Recommended if you enjoyed the movie.
I wonder if there are more similar cases of books written before the movie was filmed...