I for one would have liked to see Frodo & Sam's journey to mordor in the second and third movies abbreviated a bit. It was incredibly drawn out. Otherwise I love the movies and see no room for improvement.
* Helm's Deep went on way too long, it was like 45 minutes of battle
* Legolas's action scenes were a little too over the top for my taste (Oliphaunt tail slide, surfing on a shield). I'm not sure the iffy CGI helped.
* Poor Faramir
As far as Legolas's action scenes, are you referring to the elephant? That one was CGI, but the scene of him sliding down the stairs on a shield was actually a practical effect done with wire work. The only CGI in that scene was the removal of the wires I believe.
Yes, Faramir's story is tragic but I think that's kind of the point of his story; isn't it?
I think I sort of prefer showing him struggle with it and then make the right decision rather than just making the right decision easily. Resisting the temptation makes him more heroic.
The main one was a flashback that shows his relationship with Boromir and the toxic effects of Denithor's favouritism.
The film made him look weak, violent and rash but in the books he was the polar opposite of all three.
It did make him more human, so it's not entirely bad. In the books he, like Aragorn, is a paragon of humanity, straight up just better than the rest of us.
You have living elves that remember them originally going into the west. You have the history after they came back, including several who where there. Some know the Valar personally. You can be reasonably confident of the history. Heck, you have Maiar wandering around. And then you have Bombadil. Who is he? Nobody knows! Not the elves, not the Maiar. What does he want? To sing goofy songs. It's beautiful!