I'm aware the Grey Havens and such were in the book, and thus had a "rightful" place in the movie. But we are talking about adaptation here, and when most audiences feel the film had 12 endings and went on endlessly, then adaptation skills are duly called into question. There had to be a better "filmic" way of expressing all the stuff that went on after the Ring is destroyed. Very tough stuff to adapt, but the truth is ... the story did not end with the destruction of the Ring, but was merely 5/6's finished. That presents a valid adaptation problem, because the equivalent of the Death Star destruction is not nearly the of the story ... though it was the story's Maguffin.
Similarly, the chronology-shifting of the second two "books" make for much more difficult adaptation than the first. And I think Jackson plainly failed. His decision to present events in chron order, through cross-cutting, was a lazy and standardized choice that neglected the tale's true effect of chronology-shifting. It was not simply Tolkien's device of convenience ... it was the way in which the story must be told if you are telling the story of The Lord of the Rings. Much in the way that a remake of Memento told in forward order would not be telling the same story at all, erasing the chron-shifting of LotR negates many of Tolkien's most important story points.
Oh, and while I'm at it ... changing Faramir's character to a charlatan was up there in the big, big goofs.