There's a lot of good, in fact. Overall, it sticks somewhat closer to the book than the second film, even though several episodes are vastly inflated from the largely summarised accounts in the original. Smaug's attack on Lake-town (with a too-short reappearance by the great dragon and Benedict Cumberbatch as his voice), the gathering of the refugees and the elves before the Mountain, and very much the battle itself were all filled out.
There's also the attack on Dol Guldur, the climax of the White Council thread. Tolkien never gave a detailed account of what actually happens, though it wasn't at all how I imagined it. Still, it works well, and gives us another glimpse of the mighty Galadriel who was briefly unleashed when Frodo offered her the Ring.
As might be expected, there's plenty of foreshadowing of LOTR, from Saruman's suave assurance that the others should "leave Sauron to me" to Bilbo's growing obsession with the Ring.
This is the stage of the plot where Bilbo really comes of age morally, and Martin Freeman handles his inner struggles excellently, both over the Ring and the Arkenstone (which, like Bard's black arrow, has a lot more significance than in the book). This is contrasted with a thorough exploration of Thorin's descent into near-madness and his return, which is equally well portrayed by Richard Armitage.
The Battle of the Five Armies is the film's centrepiece, as it should be, but arguably it was overdone, as most of the action set-pieces have tended to be. It's perfectly reasonable, of course, that we should see the action itself, and what's happening to people we care about in the midst of it, but I feel it goes on for a little too long.
Possibly the highlight of the battle is the arrival of Dain, Dwarf-Lord of the Iron Hills. Most of the dwarves have Scottish accents, which fits, but it was a joy to hear Dain's greeting in broad Glaswegian and realise it was Billy Connolly. This was no noble, questing dwarf, but a brawler from the Gorbals.
Eventually, though, the whole focus shifts to a personal showdown with the orc-lord Azog and his "spawn" Bolg (the book simply calls Bolg Azog's son) featuring Thorin, Fili, Kili, Dwalin and Bilbo, with Legolas and Tauriel pitching in (giving Orlando Bloom plenty of opportunity for acrobatics). I do think this goes on too long, though its culmination is moving.
And then home to Bag End, shown much as in the book (with a brief cameo of Lobelia Sackville-Baggins) and a final scene with the old Bilbo (ignoring the fact that he shouldn't have grown old) welcoming Gandalf before the Party. And a final nice touch — the song over the credits is sung by Billy Boyd, aka Pippin.
Altogether, I don't find the Hobbit trilogy as successful as Lord of the Rings. The action scenes are overblown throughout, and some changes seem to have been made for change's sake. Perhaps Tauriel irks me most. Not that there's anything wrong with either her character as it stands or Evangeline Lilly's performance, but the romance between her and Kili just doesn't convince me. Why should a dwarf find an elf-woman attractive (she doesn't even have a beard, after all)?
More than that, though, is that she's introduced specifically for a romantic subplot. I can perfectly well understand why Jackson wanted a strong female character in the films (besides Galadriel's brief appearances) but it seems rather tokenistic that the one female character should be introduced purely as love interest, however kick-ass she might be. On the plus side, her presence helps Legolas's development and turns Thranduil into a genuine character, but that could have been done in a less stereotyped way.
Still, there's a lot to like, and I can see myself rewatching the films often enough on DVD. Perhaps I'll even watch the entire hexalogy straight through — if I ever have the odd eighteen hours to spare.