Peter Jackson has picked up the pace. He began his Hobbit trilogy at an amiable, meanderingly wayward canter, and tried the patience of believers and non-believers alike with that initial supper scene, almost an epic in itself. But this second episode commences with a narrative whipcrack – a quick flashback to Gandalf and Thorin tensely discussing their great plan in the snug bar of the Prancing Pony – and then we're off, at a tremendous gallop.

The Desolation of Smaug is a cheerfully entertaining and exhilarating adventure tale, a supercharged Saturday morning picture: it's mysterious and strange and yet Jackson also effortlessly conjures up that genial quality that distinguishes The Hobbit from the more solemn Rings stories. The absurdity is winning: you're laughing with, not laughing at. For me, it never sagged once in its mighty two hour 40 minutes running time and the high-frame-rate projection for this film somehow looks richer and denser than it did the last time around. Maybe I'm just getting used to it. Jackson has shown that he is an expert in big-league popular movie-making to rival Lucas and Spielberg. His Smaug, with its fight scenes, chase spectaculars, creepy creatures and secret stone doors opening with a grinding noise, is something to set alongside the Indiana Jones films.

The end of the second movie out of three gives us a chance to revisit that critical question: does The Hobbit story work at this great length? Does epic-i-sation risk making The Hobbit too dour? In the book itself, Tolkien wrote: "Things that are good to have and days that are good to spend are soon told about, and not much to listen to; while things that are uncomfortable, palpitating and even gruesome, may make a good tale, and take a deal of telling anyway." So perhaps Tolkien anticipated the way in which fantasy can grow exponentially, spinning substance out of itself, and become more and more serious and even solemn. Yet this second Hobbit film has real energy and charm. Smaug is of course the terrible dragon, voiced by Benedict Cumberbatch, who has usurped the Lonely Mountain and the dwarf kingdom of Erebor with all its gold, and whom the dwarves and Bilbo Baggins are on a mission to unseat. The "desolation" is the wasteland he has imposed on the country thereabouts, rather than any depression the dragon himself may be feeling. Thorin Oakenshield (Richard Armitage) is the alpha dwarf, grimly intent on his destiny: to reclaim his people's heritage and homeland. Martin Freeman is Bilbo, and Freeman's laidback, more naturalistic line-readings make a pleasing and interesting contrast to the more contoured saga-speak that comes out of everyone else's mouth, whether they are speaking English or Elvish or the guttural Orc tongue. Bilbo is reluctant to confide the truth about the ring in his possession to Ian McKellen's Gandalf, who absents himself from the party reasonably early on, leaving that visually striking group looking and feeling vulnerable. Poor little Bilbo playing a non-Snow-White to the even littler dwarves as they trail across the magnificent landscape – but who are in fact tougher, more aggressive and more resilient than him. A series of bizarre fantasy episodes, in a kind of Jackson-Tolkien-rococo style, brings us closer and closer to the mountain. The dwarves encounter Beorn the skin-changer who agrees, albeit churlishly, to help. The company finds itself lost and somehow spiritually oppressed in the forest of Mirkwood in which they get up close and personal with some colossal and very nasty spiders, which loom out of the screen in three dimensions, encasing their prisoners with skin-crawling webs. But the most uproarious setpiece comes when Bilbo, Thorin and the dwarves escape from the wood-elves' prison by hiding in barrels that are washed away down the river – which will bring them in contact with Bard the Bowman (Luke Evans) and then the vain, shifty and time-serving Lord of Laketown, enjoyably played by Stephen Fry. The barrel-chase down the river is a great sequence: a full-tilt headspinning action spectacular with orc against elf against dwarf-and-hobbit. Somehow, the whole movie has this same huge propulsive energy, whooshing the heroes onwards towards their great goal. Despite the dwarves' tough reputations, and Bilbo's expertise in the ignoble art of burglary, their diminutive size always gives them a weirdly childlike air: an air of outraged and unquenchable innocence. Bilbo's showdown with the terrible Smaug himself is of course the great finale, a narrative rhyme to his faceoff with Gollum that concluded the last film, and a satisfyingly exotic event. And all the time, Jackson's New Zealand landscape has a storybook beauty, a fitting habitat for this story which unfolds in all seasons and times of day: fallen snowflakes gather in beards, the last rays of sunset glints in fur. Jackson depicts this fantasy world with style and gusto, and I'm looking forward to the third film already.