I’ve read the book, and watched the movie, and have enjoyed both but for different reasons.
The book was fun to read, the internal monologue from Grace was fun and I honestly enjoy reading the places where the get into the details of what’s going on and why things were done in the way that they were.
The movie didn’t have time to go through all that exposition and there were a lot of things that were explained in much more detail that wound up being a single line of dialog or where quickly shown rather than explained. And for the pacing and scope of the movie that’s fine by me.
As for the movie, it was something that I really enjoyed. They nailed Rocky, and honestly he’s more entertaining to watch than the humans in the movie.
If you haven’t watched the movie, or read the book, start with the movie and then pick up the book. The book will fill in some blanks but if you watch the movie first you won’t feel like you are missing anything on your first watch.