My first direction with this was going to be 'maybe they should have called it 'the expanded hobbit'. After all, all of the major beats of the story are in it, it's just there's a whole raft of other things that have been added to.
The additions come in two categories: Canonical additions, that legitimately fill in the gaps of what everyone else was doing; and padding, which serves no purpose at all.
The padding is the orcs, the legolas and tauriel bits, the politics of Lakeland, the bits from the book that have needlessly expanded, and all that sort of thing. I maybe bias but I thought all of that stuff was rubbish; worst of all when they kept cutting away from SMAUG to some elf putting herbs on some dwarf's leg. The other dwarf had already found the herbs, so I'm guessing the whole song and dance was redundant. Good bedside manner, but it crippled the pacing because our attention was flitting between a cussing great (and beautifully realised) dragon, and some kipple that no-one cares about.
I can tolerate the canon, because I've come to accept that while it's a good idea to film it, it won't have the brand recognition to stand up as a film in its own right. So I'm not averse to seeing bilbo weakening to the ring, or seeing gandalf going after the necromancer of dol goldur.
I could go on, but my point is best illustrated in the character of Bard. In the book, Bard the bowman is the captain of the guards at laketown, descedent of the lord of Dale - the ruined city next door to Erebor. In the film, Bard the bargeman has the link with his ancestor reinforced to become his main reason of being. The changes to Bard are a microcosm of the whole adaptation, and the changes not just of the events of the story, but of the tone, of the author's voice, and what he was trying to achieve.
Here's what happens in the book: bilbo notices a gap in the SMAUG's armour, comments on it to the dwarves, is overheard by a thrush. The thrush tells Bard* where the weak spot is. Bard finally gets his black arrow out - an arrow he always retrieves - and kills the dragon.
As well as being twee, this story blatantly calls back to a similar sequence of events in the ring cycle**. Plus, SMAUG as a treasure-hoarding tomb-dweller calls to mind an enlarged version of the dragon in Beowulf. Tolkien was working in the mode of north European myths and drawing on these, and those references have been adapted out of the story; Smaug no longer wakes up when he notices a single missing cup from his colossal cache. Smaug no longer has a soft underbelly encrusted with jewels except for a single gap, but rather armored scales all over except for a damaged section. His physiology is different to Tolkien's pictures, which is a shame but I don't mind because the execution was so good. Smaug is now implied to be an agent of sauron, rather than another gollum or even a radagast: someone who has gone native, who has dropped out of the world. Another foil to the bilbo who came on the adventure.
I don't mind Bard's character being beefed up, but his change from a captain of the guards to a bargeman, who just happens to be a ridiculously good shot, is unnecessary. More importantly, the adaptation has changed Bard from a hero in his own right into yet another vengeful grandson. In the film, it was his grandad who failed to kill smaug, who dislodged the scale on his chest, and who left the final black arrow to finish the job with, as if this story needed any more vengeful grandsons*** wielding their Freudian 'father's spear/arrow/sword'. Bard doesn't need to listen to a talking thrush now, as he already knows his grandfather dislodged a scale from SMAUG's underbelly and knows where to aim. We haven't seen the hobbit 3 yet, but it's already been set up to make talking thrushes redundant.
I just want I remind people that this is a children's adventure book, with a very friendly author's voice. That tone has been completely lost. For instance, Beorn is now no longer just a random magical creature in a fantastic world, but 'the last of his kind', after those damn orcs wiped out his people.
Most of the bits from the book that are in the film are dealt with pacily and punchily; the episode in mirkwood - weeks in the book, minutes in the film - captures how you would expect an adventure film to run. They've been neatly compressed into exciting episodes and I can't wait for the fan edit of the hobbit that cuts it back down into the book form (not that it would be a particularly faithful adaptation, but at least it would be an adaptation) which I reckon would last as little as an hour and a half. On the other hand, others have been bloated horribly, although less so in the hobbit 2.
My point here, which I've been building towards, is that this is not the events of the hobbit, or the tone of the hobbit. The overall message - that you can't step in the same river twice - is in there, but it is watered down, and buried deep under an avalanche of generic fantasy shit. And its abandoned the ancestral roots of the hobbit, that connects it to its source material. It's like one of those buildings that have been knocked down, leaving the fascia, with a new core. It's not the hobbit, there and back again. What it is, and how good it is, I don't know.
*who can speak thrush because he's a descent of the people of Dale [asif that's an explanation]
**in the Seigfreid kills the dragon Fafnir by digging a pit so that he can stab upwards into it's soft and unprotected underbelly. Upon drinking the dragon's blood he levels up and gains the ability to understand the speech of birds, who tip him off at an upcoming betrayal. The same text also inspires Tolkien's cursed ring and a fallen hero's shattered sword reforged by an heir.
***also the time no longer makes sense as 200 years have passed. Perfect for a dwarven grandson like thorin, but not a human (unless Bard is numenorean too)