Ok, do not, I REPEAT DO NOT, waste your money on this. If you want to be spoiled, get the graphic novel. It will be a more in depth look at the movie in 96 pages than over 350 pages in the hardcover.
Some of the glaring flaws
1) When Order 66 is given by Palpatine, the graphic novel and movie previews show a bunch of different Jedi and hint at the outcomes. The book sums all of them up in less than 1 sentence, and not even by name.
2) The movie and graphic novel, as well as the toys, indicate the story will take part on Kashyyyk for some of it, especially with Yoda and Chewbacca. This is a two part reason, to show Yoda's true mastery of the Force, as well as introduce Chewbacca into the story. The book portrays Yoda on Kashyyyk as an afterthought and Chewbacca and Tarrful are in no way mentioned in this book at all.
The only good part about the book was the fight between General Grievous and Obi Wan Kenobi, as that was like the only non-Anakin chapter of the whole thing. While I realize this story is about the final turning of Anakin Sywalker to Darth Vader, the book was 90% focused on him, and 10% focused on how other characters view or act with him. I do not feel Lucas wrote the story this way, and I still have great faith in the movie to be the blockbuster and story we all hope it will be. I just feel this author has no concept how to write a movie adaptation.