Though it is not common for an adaptation to be better than its source material, it can sometimes happen. Lord of the Rings is definitely proof of that. Of course, Tolkien deserves a lot of credit for coming up with such an expansive and intriguing world. Tolkien treats the majority of characters with the care and respect they deserve. Yet there is one character who Tolkien could have treated a bit better. And that character is the focus here. In the end, nothing created by human beings will be perfect. And Tolkien is still an amazing writer, one who will continue to be loved for a long time.
However, for this character's sake, it's a good thing that the movies exist to fully develop them. That character is Arwen. Yes, Arwen, a rather powerful and certainly interesting character. While she is present in the Lord of the Rings books, her character is given much more to do in the movie adaptations. For example, in the Lord of the Rings: The Fellowship of the Ring movie, Arwen fights against the Nazgûl and puts Frodo on her horse, sending him to Rivendell.
In the books, another elf, a man named Glorfindel, helps Frodo. In the Lord of the Rings: The Two Towers movie, viewers can still feel Arwen's presence even though she doesn't technically appear. A severely injured Aragorn sees her kissing him, which brings him back to life and gives him hope.
And of course, Arwen and Aragorn get married in the Lord of the Rings: Return of the King movie. In Tolkien's version, Arwen and Aragorn also marry, yet it is not as exciting for readers due to the lack of prominence given to her character. For those who haven't read the books, Arwen appears in The Fellowship of the Ring and then again in the Return of the King.
At the end of the books, Tolkien devotes a section to telling Arwen and Aragorn's story. However, this section does not fully give prominence to her character either. In fact, it does not show Arwen much as an individual at all. While the Lord of the Rings movies dedicate a lot of time to Arwen and Aragorn's romance, she is shown to be heroic in her own right in that version of the story.
By contrast, in the books, after Aragorn passes away, according to the story at the end, Arwen passes away as well soon after. That does not seem like something that the Arwen of the movies would do. Of course, love is complex, and there is no doubt that Arwen and Aragorn are it for each other. With that being said, Arwen deserved to continue on a bit longer and be the hero of her own story, especially since Arwen and Aragorn had children. Children who would have definitely loved to see more of their mother.
There are, of course, understandable reasons why Tolkien wrote Arwen the way he did. It's hard to know for sure, but one reason that comes to mind is the lack of understanding at the time for female characters needing to have their own prominence beyond just being part of a male character's story.
And since Tolkien himself is not a woman, it might not have seemed to him to be anything other than a cute love story, one that did both characters justice. While the love story is cute, Arwen as a character certainly deserves better. And luckily she got it in the Lord of the Rings movies, where her character is a symbol of strength and hope.
Of course, there are two ways to look at this. Some fans might prefer Arwen's book version and might not see any harm in her portrayal there. Some might even prefer it to the movie's version of Arwen. Everyone has different tastes and preferences when it comes to fiction. And in the end, Lord of the Rings is great, both books and movies.