They also failed to adequately explain Denethor's insanity (attributable to his own use of a palantir.)
Even the Rankin-Bass animated special gets that.
I also think that the theatrical film would have been fine with Saruman's death in the first twenty minutes. I understand Jackson's reasons for cutting it -- it would have been too much action too early, and an action that paid off the last movie but had nothing to do with
this movie -- but the real problem is that it simply wasn't scripted well. I think the Saruman/Gandalf confrontation without Saruman's death would have worked better. It was really a case where Jackson's desire to do a Hammer-style scene that got in the way of his filmmaking.
RotK is the film I'm the most unhappy with. Simply changed too much from the book. The problem is that a lot of unneccessary and uninteresting stuff got extended, but the important stuff got removed or wasn't even considered.
The alterations didn't bother me a whole lot, and they're a function of the pacing that Jackson puts in place for the film. (Seriously, you're two hours into the film, and there's
still a hell of a long way to go to Barad-Dur.) The one alteration that Jackson planned that I wished he had kept was the Aragorn/Sauron single combat at the Towers of the Teeth. (Aragorn fights the giant troll instead, because that CG could fit over Sauron in the scenes.) That's what the films were building towards, why there are all the hints in the first two films that Aragorn is not Isildur and he won't fail where his ancestor did. Because Jackson backed away from the story he was telling, the climax of the film feels hollow.