The Major, in the book, is a figure we see once at the very beginning and once at the very end only. We learn a little bit about him through the other characters but he's not there talking shit every handful of scenes. With the book I had the impression he was president for life after a martial coup. Movie Major personally kills Garraty's dad so he's like a high ranking member of the secret police I guess? Hamill does nothing interesting. It doesn't work.
The book has a traditional horror story ending that was foreshadowed a bit - there isn't really a winner. It's not to say it's some screwjob where we find our Long Walkers basking in the Maui sun like Whitman, Price and Haddad. It's that to be the last walker left walking you're going to go insane or die from the stress or both. Garraty loses his mind, the end. It's a perfectly serviceable ending. In the film Garraty plans to use his wish to ask for a rifle so he can shoot The Major. It's so...small? That's all you've got? He does have an arc where he realizes that he's committing suicide the same way his father did at the hands of the state but that's kind of it. McVries wants to do something good for the world. Book Garraty wins, goes insane, movie Garraty takes a knee and McVries wins.
Imagine you're Garraty and as Jesus is taking you up in his arms to Heaven you look down and see Mister Hope and Change McVries throw all that positive change shit in the dumpster so he can go with your wish and shoot The Major. Also your mother just watched her son get gunned down in the street after a similar fate befalling her husband years prior. Sucks to suck I guess. It just doesn't work. There's too many "you're my brother naw you're my brother" back and forths between Garraty and McVries and the film tries to use it's score too many times to add emotional weight to scenes. The general pacing on the ending itself is dreadful. It needs take a quarter of the time.
In general it's still surprisingly faithful to the book and it wasn't a chore to sit through. I didn't like that so many of the towns they went through were empty as viewing the event was not allowed outside of some exceptions. As a contrast to the walkers themselves you need to see everyone else having a great time on a beautiful day as the best parade of the year comes through their city. It makes it everything way more fucked up than just having the whole thing be somber.