Saw this tonight, and was 2 hours well spent.
Whereas AUJ was slow in periods and felt a bit padded, DOS was fast-paced. Once the prelude is over, the film starts running and doesn't stop.
There's a lot to like. Smaug is excellent, drawing well from the books to be a unique character. A dragon very much in love with himself (and gold). Thankfully the CGI for him is a lot better than in the trailer. I also found Jackson's depiction of the Necromancer very interesting, and it really works well in terms of going from in the void to a spirit to the flaming eye, and in doing so shows how he could have then retaken physical form. The wood-elves feel like a race of their own, rather than repeats of the Rivendell and Lorien elves, and Thranduil is well played with a nice mix of majesty and haughtiness.
In terms of negatives, the LOTR repeats felt too obvious - whilst Tauriel and Afrid are characters within their own rights, they are clearly mirroring Arwen and Wormtongue, and the references to Gimli and kingsfoil/weed felt a bit forced. I'd heard moaning about the 'there could be anything down my trousers' joke and perhaps that ruined it for me, but it felt a bit crude for the films. Legolas gets a lot of air-time and by the end still feels very different to the character we know from LOTR. But on the plus side, they got rid of the bright blue eyes!
Action scenes are generally well worked and entertaining (as you'd expect), and have enough choreography to make them interesting and humorous, though the camera work was often nauseous, and unnecessarily so. And people seem to keep on surviving ridiculous falls!
In terms of dwarven character development, with all the new faces (Beorn, Thranduil, Legolas, Tauriel, Bard, Master of Laketown, etc), the main dwarves were Thorin and Kili. Thorin's pride has increased as they near their goal - like in AUJ it leads to some unwise actions, and knowing what the third film has in store (from the book content), it should be a fairly smooth transition to the dwarf that then cuts all times with the people who helped him and locks himself in the mountain. I'm not sold on the whole Kili romance with Tauriel, it just feels silly and (as mentioned) a play on Aragorn/Arwen. Balin is the ever-able supporting dwarf, well played by Ken Stott - you can see how the pains of his life and leaving Erebor have made him the wise one of the group. Bombur and Dwalin were focused on less than in AUJ, the rest were the same.
The splitting up of the dwarves will undoubtedly annoy purists. From a storyline perspective, I can see it helping the lead-up to the BOT5A with an emphasis on aid and not just on getting their share of the treasure.
And the ending... it worked in that it made me want to watch the next film immediately. But it's not a TV show that will resume next week, we have to wait 12 whole months and the film as a stand-alone production feels a bit unfinished.
So in conclusion, it was a really enjoyable few hours. The LOTR trilogy remain some of my favourite films and I saw all three having not read the books and even managed not to read any spoilers (though it was easier in the dial-up days to avoid it), so I didn't have any preconceptions about characters and events. But even if that is slightly holding me back from really loving the Hobbit films, I think it's stating the obvious to say that we're still not quite at the LOTR level - but we're closer and I'm still really looking forward to the third and final film.