The movie was much better than the book
Typically, it's the other way around. But I just finished the book and didn't like it anywhere near as much as the movie. Which is strange, because I liked Persuader a lot. One Shot was a real slog, though. The plot was too slow and there were too many side characters who weren't really all that necessary: Franklin, Eileen Hutton, Rosemary Barr, Ann Yanni. Christopher McQuarrie did a fantastic job adapting and even improving the story.
There were things in the book that I just can't understand why Lee Child put in there. For example, why did Child include Reacher making love to Eileen Hutton at the hotel? Especially when he was on the run for Sandy's murder. If you're on the run, are you really going to stop and have fun with some woman you knew from the army? Thank goodness the movie got rid of that pointless subplot and character.
Plus, Ann Yanni's character was absurd. She just gives up her car to a wanted murderer and doesn't call the cops afterwards? Yeah, right. Beyond that, Child makes a big deal of Reacher evading Detective Emerson and later getting arrested. Then he just goes scot free a short time later because Yanni gave Reacher an alibi, claiming she slept with him. Just unbelievable.
The final shootout in the movie was much more exciting and satisfying than the house assault in the novel--which felt like a retread of Persuader's finale. And Reacher didn't even kill Zec in the book. So frustrating.
I'd suggest skipping the book and sticking with the movie. IMO, it was a far more enjoyable version of the story.