Now, I watched the movie before I read the book, and before I knew who Jack Reacher is.
But the 1 thing I felt from the very beginning of the movie, were 2 things.
1. He's too short. The story literally calls for a beast of a man(tall, strong) it's a great piece of writing the physicality into the script.
2. He's not difficult enough. Cruise is 'Mark Harmon light' in the movie, and you'd expect a much heavier personality, a little meaner too.
The screen-play(based on One-Shot) was very strong(so strong, that it even exposes Tom Cruise as a problematic-fit).
Jack sees Barr's arrest on TV, buys himself some new clothes, and head to Pittsburgh to 'bring him his justice'.
Barr gets a beat-down, so when Reacher reaches town, and talks to the DA, and Police, he ends-up with too many questions, not enough answers, so he decides to help Barr's lawyer, in order to have access to the details of the case.
The rest of the movie has great progression, and arc, the fight-scenes are a little-light(again because Reacher in the books is a 6'05/250 lbs BEAST(think Dolph Lundgren), and Cruise clearly isn't.
The story holds though, if you can see it as an independent, rather than connect it too much to the book. Because the story is great, the movie is solid, Tom Cruise just isn't 6'05/250 and a dirty-blonde though.
I'd love to see a TV-series of Jack Reacher, because I think it might be more suitable to the vibe of the books, than movies.