The LOTR movies are great movies, but are pretty poor adaptations. I don't mind changes which were necessary due to the medium (e.g. cutting Tom Bombadil, which just would bloat the movie without adding anything crucial to the story). But Jackson went beyond that and made changes (for example, having Faramir give in to the temptation of the Ring for a time) because he disagreed with Tolkien's story (that specific change was explained in terms of Faramir's character in the book "doesn't work with the way we are trying to portray the Ring"). That's crossing a line, imo.

The Hobbit movies, on the other hand, are both bad adaptations and bad movies. Truly awful stuff.