I read this (in audio book form) after watching the miniseries on Hulu. If you have watched the series I recommend reading the book; if you have not watched the series then just reading the book is plenty. There are several characters who appear in the book but not the show, and many key differences between characters that appear in both.
This was the first fictional book by Stephen King that I have read. After this I feel slightly more justified in reading one of his nonfiction books that has been on my list for a while On Writing.
One theme of the book that I appreciated is the desire to see order or conspiracy in an essentially random event. Readers of this book would likely also enjoy The Lady or the Tiger and Mrs. Paine’s Garage.