Hello.
Like others before me, I agree that there is no parallel to comparing books to movies. Two different mediums requiring two different ways to achieve their goals.
Now because of the following, I must surely be in a minority:
Although I have played/dm'd D&D for 14 years, have been a member of the SCA, and have enjoyed many a renessiance fair, I have NEVER read any of Tolkien's works. That's right--Not a single one. (Please put away the torches.)
I have viewed FOTR and TTT without having any foreknowledge of characters or their motivations. The movies are simply the best fantasy movies, if not the best movies regardless of genre I have ever seen. I have held my breath, gripped my seat, shivered, cheered, and even cried during these movies. (I have seen FOTR 15+ times, and will probably watch TTT as much when it comes out on DVD.)
Many people have described how audiences would be left wondering about continuity because certain scenes weren't included, or certain events were changed, but from someone who never read the books I can safely say that I was never left wondering about any of it.
Now my opinion on the Boromir death scene:
I cried. I admit it. Like I said before, I never read the books, so I had no idea he would die. Sean Bean's performance during this movie was great, but the death scene brought it all together. I honestly would have had trouble with him breaking off arrows, or even taking any more than they showed in the movie. The movie scene felt very plausible, while that other description makes me think it would only work if they had Dwayne Johnson ala the Scorpion King (or Arnold back in his buff Conan days). Boromir was a man. No magic and no superpowers. At the end of FOTR (and even now after seeing it so often), he remains one of the most heroic characters I have seen in any movie.