While I agree with your points technically, I don't let the changes bother me. I rationalize that they didn't change the goal of the movie, only some of the means of getting there. The tactics, not the strategy, if you will.
For instance, let me analyze one of the biggest changes: the substitution of Arwen in place of Lord Glorfindel. In the book, Lord Glorfindel and his magnificent white horse meet Aragorn and the Hobbits on the road to Rivendell. He helps to ease Frodo's wound a bit, hurries them along the road, and eventually gives his horse to Frodo so that Frodo can make it across the river before the Ring Wraiths get him. So, what is necessary in this scene?
Is Glorfindel necessary? Well, he's a fairly minor character who plays no further significant role once Frodo is across the river. He eased Frodo's wound, but it can be assumed that most any Elf can do that. What is really needed in this scene is the horse, because that is the means for Frodo to escape the Wraiths. Again, any Elf can ride up on a horse.
So if Glorfindel himself isn't necessary, who can we have in his place? Well, most any Elf will do... but how about one who is necessary to the story later on? An Elf who has quite an important role in the story, if only in the background in the book. Arwen, for instance. After all, it's for her sake that Aragorn is striving to be king in the first place (it was a condition placed on him by Elrond... no marrying my daughter until you're the king!) Introducing Arwen at this time accomplishes several things in the movie: it lets the audience meet her, it lets the audience know she's involved with Aragorn, and it lets the audience grow more sympathetic to her character by seeing her help rescue Frodo, than it would if they only saw her lurking in the background at the Council meeting.
Analyzed in this way, switching Glorfindel to Arwen makes perfect sense, for a movie that must be presented in a limited time, with a limited cast, and a limited budget. That's why I can forgive this and other changes made from the book, because I see them as being necessary for the movie adaptation and more importantly, not changing the overall spirit of the books.
Now, if you want to talk about a movie that diverged wildly from it's source book, we can talk about Starship Troopers....
While I disagree with your analysis, I appreciate the thoughtful response. I still believe that Arwen was placed in that position to pander to feminism, and I am tired of our society pandering to feminism. I also believe that Frodo should have made the ride alone as he did in the book. Making the ride alone shows the hobbit toughness that we admire. His stopping on the opposite bank (in the book) shows the struggle he faced as the wound and the ring overcame his own will. Your thoughts make perfect sense from the movie-making perspective, and if this were the only point that bothered me, my feelings about the movie would be different.
I've never read Starship Troopers and only vaguely remember the movie. I remember being particularly angry at the 90's movie version of Last of the Mohicans. Whoever made that movie butchered the character of Natty Bumpo horribly. On the other side, I actually like the Jurassic Park movies as much as or more than I liked the books.
WFTR
Bill