For those that have not yet seen it, there are exactly two ways you will enjoy this. Firstly, if you haven't read the book, and go into the movie expecting it to be long, you will probably enjoy it. Secondly, if you have read the book, as well as all the appendices then you will enjoy this movie. If you've just read The Hobbit then there is a lot added to this movie that will distract you.
None of these changes are necessarily bad, many of them will excite the seasoned Tolkienite since a fair share of what we see is material I doubt anyone expected to see put to film. Furthermore the rest of the added material, with the exception of Azog's story, that was just plain unnecessary, comes from events that happened in the background of the book. In fact, Peter Jackson and crew expand on what amounts to nothing more than a throwaway line at the end of The Hobbit and use it to tie The Hobbit and The Lord of the Rings together.
That being said, while I agree that we don't need three movies of this, I'm still excited to see everything that is added. I have the patience to put up with three hour long movies, so I intend to enjoy it wherever possible.
Out of all the changes, the most expected, and most necessary, was in the dwarves. Except I can't really call them changes. Rather I would say they are improvements. In the book, with the exception of Thorin, Balin, and Bombur, none of the dwarves have any kind of personality. In fact, Tolkien just uses them in the same way they use Bilbo. They're numbers to make the lucky number aspect of the story work. In the movie they are not only given their own looks, but their own personalities, some of which are surprising and welcome. While several of them follow the standard dwarf stereotypes, some, especially Dori and Ori, work outside the box to give the company a more well rounded feel.
The inclusion of many of the original songs are a welcome addition to the movie. And these are surprisingly well put together.
On a second walkthrough I have to say that the early parts do drag on, mostly the parts after they leave Hobbiton, until after they leave Rivendell. While I did not hate the added parts, I have to say that they were easily the weakest part of the movie.
Easily my favorite part of the movie was the music, and while a lot of it was recycled from The Lord of the Rings, I found that the main theme of the movie was good enough to make up for the lack of a completely new soundtrack.
My biggest concern for this movie, lies in rewatchability. As much as I love The Lord of the Rings it's a bit difficult to rewatch them years later, considering how many times I've watched them. I think with The Hobbit there's a lower chance of me rewatching the movies as much. Granted I can't say anything about the other two, but this first one probably won't be one I revisit too often.
Overall though, I really liked this movie. It might not be as enjoyable for non-Tolkien fans, but for me at least it was great. I'd highly recommend it to anyone that doesn't mind really, really, really long movies. And likes hobbits and dwarves. This movie is entirely for you.