Riddles in the dark
This is by far the best part of the film, probably because it stayed most true to the book. And by that I do not mean that nothing was changed or added, but those are only minor changes and, in my opinion, a valuable addition. The addition comes in the form of the small Goblin that falls along with Bilbo. Whereas Bilbo lands in a concealed place, the Goblin lands in the open and we get to see Gollum dragging him back to his island to be eaten, he also loses the Ring in this process which Bilbo picks up. What this adds is showing us how Gollum lives, how disgusting he is in a way, we see him smashing the Goblin to death with a rock, we hear his evil side talk about skinning it. For me that really set the tone for the situation Gollum was in.
When a little later the riddles begin the choice has been made to show the twofacedness of Gollum that was present in the earlier films. This is also an addition, in where the good Gollum (or Smeagol) is really happy to play games with Bilbo, whereas the evil part just wants to eat him. Although this is of course quite a major invention of PJ, I feel that it is one that does justice to the creature of Gollum and gives him more depth without destroying what was there. Most of the riddles from the book are in there, and all in all the scene is just done well. Also the escape that follows is true to the book, although Bilbo does not have to squeeze through the gate, but gets stuck earlier. Also the choice not to kill Gollum is portrayed rather broadly, which I find rather understandably, since it is such a powerful motive that also plays a big role in the Lord of the Rings.
After he escapes we see Bilbo return to the Dwarves, that wonder why he came back. He then gives the explanation that he of course wants to go home, but that they do not have a home and he wants to help them reclaim it. Another purely invented motive by the film makers, and to my taste one that need not be there. Bilbo gets back to them because they are the people he knows in this big scary world, moreover they are his friends. On the whole scale of changes made, and with in the back of the mind the uninformed viewer, the choice to give him this motive can be understood.
Out of the frying-pan into the fire
And then of course the Orcs, Azog at their head, show up again and the company starts to run, kill a few Orcs and climb in the pine trees. Yet other than in the book, the Wargs are not daunted by this, instead they just push over the entire trees, until they are all in one tree at the edge of a cliff. Gandalf starts throwing down the burning pine cones, which scares of the Wargs. Their tree however starts to topple and they hang of the cliff, ready to fall to their death. Now here the need is felt again (just like in the FoTR) to have insects be messengers to the Eagles, so we see Gandalf sending of a moth (or butterfly). Yet, as in every good action movie, we need a stand off, so Thorin grabs his sword and starts walking over the tree towards Azog, then charging at him. Azog kicks Thorin's ass, but just as his lieutenant wants to cut off is head, Bilbo runs up and kills the Orc, saving Thorin. Then the Eagles show up and save them all, carry them to Karrock, Thorin thanks Bilbo, they see the lonely mountain of in the distance, the end.
So what has happened here. A scene that depicts them sitting helplessly in the trees, getting smoked out by the Orcs and Wargs underneath, is transformed into another battle. In this battle Bilbo suddenly becomes the saviour of Thorin and easily kills an Orc. The whole dynamic of Bilbo and the relationship between him and Thorin is changed. In my opinion this is the result of the (and I know this can be a dangerous word) formulaic approach taken to this film. It felt the need to explain everything all the time, and give us grand set piece battles that were not in the book. And why were they not in the book? Because they happened much later in the story. And why did they happen much later in the story, because that is the story arc. But because you just take a few chapters and try to make a film out of it, the need was felt to create a similar arc, complete with the drama that comes with it, within this one film, despite there not being anything of the sorts in the source material.
All in all I feel that the film has some nice depictions of the world of Middle-Earth. What is completely missing though, is the atmosphere of the Hobbit, the feeling of being a group that pulls through everything together and grows as a group in this way to eventually achieve their goal, even though some strive on the way is required. Here everything is presented as if it is on the same scale as the adventures of the LoTR were, which they are not. They are just a small group, that can't fight of thousand's of Goblins, they have to rely on stealth and trickery. In the end I think that is what simply has disappointed me the most; whereas with the Lord of the Rings I saw the changes and still felt like I saw the awesome world of Tolkien come to live, here I feel like I see CGI and fighting, formulaic set pieces that 'progress' a character as you learn in storytelling 101, and do not feel like I'm watching the Hobbit come to live.
Lastly I am especially afraid that the whole character of Thranduil is going to be the one most malformed by the end of the three films. He has already been portrayed as an odd and heartless elf, his capturing them and then later coming to claim gold will only make this worse I fear, but we'll see I guess.