It's an interpretation to me. I see it as a different entity to the book. Differences from the book are not a flaw to me; same as differences in superhero movies to the comics.
The fact that it is different, in and of itself, to me, isn't the issue.
However, if they are going to use the brand identity, I expect them to at least keep major themes intact. I can then look at the impact of changes on those major themes, and ask if they are improvements, detriments, or do not make much of a difference to those themes.
That they've added material, and it has a notable negative impact on some of the major bits I expect them to be using, speaks to me of a failure in editing. Change for the sake of change is not a great idea - so changes should be made *for purpose*.
So, as I said, action scenes of the purpose of making it kind of a must to see in the theater I can get. Addition of a major female character for purpose of allowing the material be more accessible and acceptable to a modern audience, I'm fine with. But then making that female largely there for purpose of having a romance with what was originally a minor character? Women don't exist for the purpose of being in romances, so doing it this way rather defeats the purpose of the addition.
Making it so very clear that the Necromancer *is* Sauron outright makes some of the action in the previous movies difficult to justify! How is this serving any purpose well?