Small changes? In the most recent movie, three of the most prominent characters were not even *in* the book, and the plot was distorted beyond recognition.
The very first LOTR movie was ok, the extended version better.
The rest, including all the Hobbit, have been horrible.
The only change Im personally aware of was the affection between the elf and dwarf. Everything else is part of the Tolkien universe in one of his books somewhere.
Like it or not, though not many females are in the Tolkien books, they exist in real life and they need something to keep them interested in wanting to see the movie. :)
I don't have a problem with that, in theory.
Most of the stuff with Dol Guldur and such is actually in the Tolkien mythos, primarily in the appendices to LOTR.
The problem is that The Hobbit is a children's story. It's told from the perspective of a funny little person, quite unsophisticated. For most of the story he doesn't have a clue about the larger picture of what's going on around him.
What PJ has attempted to do is take this small, sweet story and turn it into an epic, with the scope and scale of the LOTR movies, which I thought he in general did quite well.
However, I fell asleep in the most recent Hobbit episode. Too much video game nonsense.
My complaint is not so much that he expanded the story, but that he did a poor job of it.