More than anything else, I was angered at the switch in how Gandalf and Aragorn looked at Moria versus the Redhorn Pass. In the book, Gandalf wanted to go through Moria because he believed that the path through Moria was best for the fellowship. If he was aware of any threat to himself, he didn't talk about the threat and didn't let the threat change what he wanted to do. Aragorn argued against Moria because he saw a threat to Gandalf and was afraid of losing Gandalf. Part of his motivation was fear of losing a friend, and part was fear of what Gandalf's loss would mean for the fellowship. In the movie, these attitudes were reversed. In the movie, Gandalf saw the threat to himself in Moria and argued for the mountain pass in order to save his own life. Aragorn also saw a threat to Gandalf in Moria but argued against the mountain pass because he didn't care.
The difference is in the character shown by the characters. In the book, each is concerned first for the well-being of the fellowship and in Aragorn's case, for the well-being of a friend. In the movie, each is concerned for his own safety. The positions they took in the book portrays them as much more noble men. The positions in the movie might make them more realistic to modern society, but I like noble characters in a fantasy book. Above all else, I can't forgive Peter Jackson for this change.