I was eager to see this movie because I really liked the book. I read it before I had any exposure to statistics. So it was kind of an eye opener for me. Yet it wasn't too difficult to understand. That is one of the reasons Michael Lewis is such a great writer. He makes things easy to understand without dumbing them down too much, all the while keeping the flow of the story he is trying to tell.
As with the movie The Blind Side, which was another book by Lewis, it would have been really difficult to get every nuance from the book into the movie. We see a little bit of Billy Beane's career as a player and how that influenced him as a GM. But it wasn't really fleshed out. And we see a little of the new way in which they start thinking about the game, the Bill James influenced sabermetric approach. But it didn't seem as carefullly constructed as the book.
But that's just the reality of adapting a movie from a book. I'm sure even as great as The Godfather movies are they miss some nuance of the book. Having said that, I enjoyed the movie. Brad Pitt and Jonah Hill were good. It did a pretty good job of making us care about the team and Beane. And it was funny enough to carry us through some slow parts.
I agree with Matt Yglesias that it could have used more math. They didn't need to walk us through the equations they were using to calculate probabilities of runs and wins. But they could have explained the logic behind what they were doing in more detail. They get the concept behind valuing OBP, or on base percentage, across pretty quickly and easily. But they didn't go the extra step in explaining why OBP was undervalued and why it would lead to them winning more.
Fans of the book should like it if they have the right expectations. I think people who have no idea about the book should like it too. They clearly tried to make it accessible to those people. And I think they succeeded. At the very least people should like the underdog story of the A's trying to compete with the Yankees and big market teams.