Black and White - Absolutes Revisited
In the books, Faramir is the foil to his brother Boromir; where Boromir is rash and impulsive, Faramir is valorous and reasonable. In the movie version, the two brothers display identical tendencies toward the ring. They are both brave, but they are both willing to seek power without concern for virtue. This was very disappointing, because it took away a portion of the innocent hope brought about by a truly good man in desperately evil times. It deprived the audience of an emotional respite from the fighting, in the interaction of Frodo with one who understands and respects his mission.
Ditto with the Ents. Instead of slow but virtuous, the Ents are unwilling to help until personally affronted by Saruman. Whereas the books represent the common mission of all of virtuous creatures from all corners of Middle Earth, the movie never makes it clear that the Ents know or care if they are on the side of virtue.
When Wormtongue is displaced as the advisor of Theoden, readers expect the king to march to war, not to cower in a fortress. Theoden's return to virtue is indiscernable in the movie, taking place too little too late. The only advantage of this is more time to watch Strider on the big screen.
With regards to Aragorn, the movie takes the seldom-mentioned, yet extremely pure love between Aragorn and Arwen, and taints it by giving viewers doubts of their affection for eachother. They make Aragorn appear interested in Eowyn, and make us think that Arwen is leaving for the isles in the west. Besides the fact that Arwen is seldom mentioned until the very end of the series of books, Tolkien gives his readers no reason to suspect that either of them considered straying. There are enough plot twists left out of the movie; Jackson did not need to add one, taking away a beautiful romance in favor of more female screen time.
In summary, readers always take a risk when watching the movie version of a favorite book. The battle of Helm's Deep is a feat of incredible proportions, and the characters are generally lovable, honorable or revolting, as they were meant to be. But a little bit of the magic is missing when the good guys take this much persuading to come to the aid of the fellowship.