As adaptations go they never get them right, even the best case scenario as in Peter Jackon's Lord of the Rings leaves a lot to be desired.
Because there is no 'right.'
List any complaint you have with LOTR films, say any change you'd make, and some other fan will say "no that's totally against the spirit of the work!!"
Actually Since Tolkien is the author the author is where to look.
They got away with abominable changes because he sold the rights. But early on when they wanted to make films he was against any and all changes.
That is Why the film is Peter Jackson's Lord of the Rings and not Jrr Tolkien's Lord of the Rings.
The films came out of the merchandising arm of Saul Zaentz company called Tolkien enterprises which has nothing to do with the Tolkien estate, if it did you could be rest assured Christopher Tolkien would have vetoed any and all changes to his fathers work.
I am glad Christopher Tolkien has the Silmarillion protected from Hollywood and the rest of Tolkiens writing, except for the finished manuscripts of the hobbit the lord of the rings and its appendices. Zaentz has no rights to history of middle earth or the silmarillion, or the drafts of the hobbit and lord of the rings and other middle earth material.
The bare material hinted at in the appendices is not enough to make a second hobbit film, so jackson and co are making shit up that is not in any tolkien text.
If Tolkien had lived so long i think he would have kept authorial control, when he sold the rights for cash there was no chance of them being made into films as no studio back then would spend upwards of over 50 million dollars, nor was the material worth billions in term of a possible franchise.
The Tolkien estate was livid with the changes but more than happy to accept the royalties which they had to sue to collect and then have settled out of court.