If you've read The Fellowship of the ring, you'll know that Arwen's role was greatly expanded. She managed to get from a mention in one measely paragraph, to taking Frodo across the Bruinen and having a scene of her very own where she gives up her immortality to Aragorn. The differences don't stop there. In the books, she comes across as more of an "indoor girl", not one to neccesarily know how to use a sword. In the movies, she is appointed a more Xena type role. I think this takes away from one of Tolkien's many points, since Aragorn went for Arwen, the "indoor girl", as opposed to Eowyn, the woman who does the sword "thing".Tolkien's point that I am talking about is the fact that Aragorn went for a non sporty kind of girl, as opposed to a headstrong Eowyn figure. He preferred a woman who didn't want to have anything to do with swords. Arwen clearly has many sides, some more genuine than others. I personally prefer the book version, mainly because that was how Tolkien wanted his character to be, although I do appreciate and love Peter Jackson's Arwen as well.