down the true story a little compared to what really happened. Of course, the movie still took a lot of liberties in regard to the romantic relationship with his wife, his court martial, etc. In terms of his heroic acts and miraculous things surrounding them, however, they left a decent amount out of the movie. I read an interview in which Mel Gibson said they did that on purpose because they didn't want audiences to be sitting there thinking, "No way that really happened!" and getting distracted.
If you read about him or watch one of the documentaries about him, the story sounds too incredible to possibly be true.