Okay, so I know this movie isn't technically based on a book, but since it uses Tom Clancy's characters, I felt like it is the descendant of the Jack Ryan books.
I know that sounds like a lot of backstory, but in reality, it takes up maybe 20-30 minutes of film. The rest of the movie deals with Ryan's initial CIA assignment, which soon has him traveling to Russia. He is a bit out of his depth, but to me, one of the best parts of the movie was watching Ryan grow into his role as an agent. As he is told at one point in the film: "You're no longer an analyst. You're an operative."
Chris Pine does a nice job filling Jack Ryan's shoes. Ryan is a well-known character, and Pine has the acting and action chops to do this role justice. Kenneth Branagh was a nice treat as well--I've always liked him, and it was a delight to see him in the film, which he also directed. Overall, I enjoyed this origins story, and I hope they continue to make Jack Ryan movies in this vein.
Have you seen Shadow Recruit? What did you think?