i agree that he sacrificed fidelity for structure--but it all comes down to this: what would make a better film--fidelity or structure? it's an interesting concept to discuss: is it possible to change a great work of literature into a great film and still be completely true to the original work?
Well, where you stand in this dichotomy all comes down (this sounds somewhat grandiose, I realize) to where your loyalties lie...if the movies are to be a tribute to the books and a view into their incredible scope and epic tale, they should be fairly faithful. I say fairly because, as Rhys-Davies and Josh point out, some concessions to film have to be made. But (and this is the second part of the 'loyalties' thing) if your loyalites lie with Hollywood and everything it encompasses and values, then your objective is to make a movie that will sell. As a Tolkien fan (fanatic, as some would have it), I would like to see a movie that is altered to be the best cinematographic portrayal of the books possible, not the best-selling movie possible. However, I admit that these people want to make money, and though I don't want to malign Jackson by suggesting he doesn't care about Tolkien's vision and is only in it for the dough it's fairly obvious that he made some choices due to studio pressure or a desire to make the movie fit into the traditional Hollywood mold, and that others of his choices were influenced perhaps unduly (and perhaps not) by Hollywood cliches.
I won't rehash my gripes with the movies that are out or my complaints (as yet unfounded, of course, though more-or-less confirmed) with RotK, but I stand firmly on the ground that fidelity should be considered as tantamount and structure should follow fidelity's dictates. I believe Greydanus said it well when he mentioned that most of Jackson's 'sins' in RotK were of omission (leaving stuff out) rather than comission (putting extra stuff in). The former generally causes less gnashing of teeth than the latter (though of course the removal of the Scouring will undoubtedly be a sore point among some).
On the whole, I think Jackson has done an excellent job, and I am not anticipating disappointment with the last installment. But I did want to point out that Rhys-Davies was wrong on that point and I, for one, wish Jackson HAD focused on fidelity a bit more than he did.