It's been a while, but the film followed it pretty closely from what I remember. The book has more detail on the background and the Journey before Ibn Fadlan meets the Vikings, and the final battle is different. The film also trimmed down the search for the Wendol's caverns, including the scene where they get information from some dwarves. And there's an epilogue written in faux scholarly style that explains where the Wendol came from and what they are.
