Haven't seen ROTK yet... I have to get into the right space for these things as the first one left me a complete basket case. My son had to guide me out of the theater as I couldn't see..
Tolkien's original work is a truly epic achievement- read the Silmarillion, the Lost Tales and all of his other "out-takes"and publications, and you will truly appreciate the scope of what he did. Jackson HAS done an amazing job with it and has had to make decisions in much the same way Tolkien himself in order to present a coherent final product. I don't approve of all the decisions Jackson made, but perhaps we might have preferred Tolkien making different choices in his creation if we had knowledge of his original intentions and processes?
My BIGGEST objection to Jackson's interpretation is the lack of music as an integral part of the characters' culture.Tolkien based his people on the Northern Europeans, all of whom have passed down history and mythology in musical form through the oral tradition. In the books, they naturally respond to their environment or a particular situation with a song or dance. Perhaps Jackson didn't want it to seem like a "musical" but, really a song around the fire, or as encouragement, or as a battle cry would have been appropriate! The scene where the Rohirrim sing as they go riding off was tremendously stirring in the book and felt like "just another battle" in the Two Towers movie. My son tells me it's much the same in ROTK.
   I'm really surprised that, on this forum for folk music, nobody else has said anything about this glaring omission. Perhaps I am more sensitive because my interest in Tolkien as a teenager is one of the reasons I make my living as a folk musician today (sources and all that)
Best- Julia