Well, as a Stephen King fan, I hated what they did from the book.
First the almost unimaginable amount of swearing. I don't even dislike swearing in a movie, but it was just so gratuitous.
More importantly, it's what they did to the plot. So in the book, it's not his mother that he's going to see in Freeport. It's his girlfriend, she's his emotional core. There's also no concept of revenge in the book. In an interview,I saw with the director, he said that you couldn't have revenge be the motivation of the winner. Well in the book there is no motivation for revenge and Garraty wins,,, so the revenge change basically made them change the ending of the movie. And then they had the winner exact revenge anyway. Plus,because they made it his mom instead of his girlfriend his mom has to watch him die on TV.
And then Hollywood being Hollywood, even though McVries likely wasn't black in the book, they change it all enough so that the gay black man ends up winning in the movie. And I say that really liking what they did with McVries' character. In the book he wasn't from a broken family. He had an intact family, but they made it more sympathetic in the movie, which was fine and the guy who played him did really well.
Sidenote, in the book, they actually started at the Canadian border in Maine and make their way all the way to Massachusetts I think. Which might've been more interesting in the movie, but I understand for that piece why they did what they did.
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