A lot of people watching the show were predicting O'Donnell or Dixon were corrupt. It turns out no one from the 110th was corrupt. The only tension was the belief that Swan might've been corrupt but that was just a red herring. But I don't think that ever happened in the books, and I don't think Lee Child would've allowed such a change.
FYI, Alan Ritchson confirmed that Season 3 is based on Book 7, Persuader, and Neagley will be back. So it looks like Neagley is going to be the main recurring character throughout the show besides Ritchson as Reacher. Lee Child in a video did talk about how in the books, there's no necessity for a supporting cast but that's not the case for an ongoing TV series.
I liked Dixon/Reacher relationship, but it was all just sexual tension they needed to resolve. That said, I wish they gave it a similar ending to the book with Dixon leaving Reacher like $100K and a coded message to her home address. Kind of like "Hey if you ever want to see me again, look me up."