Here's my take for what it's worth. The books are all excellent but they are little more than an allegory of a knight errant righting wrongs. Lee Childs has admitted that if you look at the books logically they fall apart because no person could end up randomly walking into these sort of situations routinely.
Reacher is smart, and interesting, but the real draw of the books is little more than Hulk Smash plus some fucking. That's a formula for sustained success.
As for the actor they chose, I thought he was too wooden in the first few episodes but by the end really embodied the Reacher character. He was physically capable of pulling it off, but more importantly to me, he was able to act in a way that brought Reacher to life. One hangup I've always had is how a person who is basically a psychopath of the highest order can interact with normal people without coming across like a total sociopath as well. And this guy pulled it off. Funny, charming, arrogant, kind. Good show.