Looks like Cumberbatch nailed Smoug as I was hoping he would. This is the first detailed review I read. Warning there are minor spoilers in the long full article so I will just quote the highlights.
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http://www.ign.com/articles/2013/12/07/the-hobbit-the-desolation-of-smaug-review
First things first: The Desolation of Smaug is much better and more entertaining than its predecessor, The Hobbit: An Unexpected Journey. This film clips along at a fast rate, upping the action and the suspense in a way the walking-and-talking first film often failed to. Everything just works better this time out: the battles, the character interplay, the visual effects, the tone, and the energy. If you were wary of returning to Middle-earth after An Unexpected Journey, fear not; The Desolation of Smaug is a superior Hobbit movie in every way.
For a movie nearly three hours long, The Desolation of Smaug hauls ### from beginning to end, from its Western-style flashback opening to its serial-like ending. The film's brisk movement largely works, although there are a few hiccups and odd, choppy editorial choices around the time we meet Beorn that mar that nearly perfect pace. When the end credits finally roll, you truly are left wanting more.
However, it's really Cumberbatch who gets the biggest bragging rights amongst the supporting cast and new players. His rich baritone gives Smaug a gravitas and regal bearing befitting the legendary beast. (Cumberbatch's other role as the Necromancer is really more of a visual effect here so perhaps it will pay off more in the next film.) Unsurprisingly, the teasers have revealed only a fraction of what Smaug is like. There really haven't been a lot of great movie dragons, but Jackson and WETA have created a doozy here in Smaug.
The Hobbit: The Desolation of Smaug is a rollicking piece of epic entertainment, superior to its predecessor technically and dramatically. It atones for the rather lackluster first film, and generates excitement for next year's concluding chapter of the trilogy, The Hobbit: There And Back Again.
THE VERDICT
If you were disappointed with The Hobbit: An Unexpected Journey then The Hobbit: The Desolation of Smaug is the film you've been waiting for. It's a breathlessly told, action-packed crowd-pleaser that restores the luster of the saga for those underwhelmed by its predecessor and leaves you excited for the final chapter in the trilogy.