This is the best movie I have seen in a while! I watched it twice in the same day.
I will state right up front that this is a "foreign movie." Made by award-winning Russian filmmaker Sergei Bodrov and filmed in China, Russia and Kazahkstan, it has subtitles. But don't let this put you off. (Start using subtitles on every film and you won't even notice them on foreign films.)
The "Mongol" website at http://www.mongolmovie.com/ (click on About the DVD) gives lots of great information about the history of the production, director, cast selection, filming locations, etc. So go there for more detail.
The movie is based on scholarly research so should be a fairly accurate depiction. JUST WATCH IT -- your image of Genghis Khan will never be the same!