A year ago, I said that the biggest problem with The Hobbit: An Unexpected Journey was that it was too much of a good thing. Having just seen The Desolation of Smaug, I think the same may be said of this middle chapter of The Hobbit trilogy. Minus the phrase "of a good thing."
Much has been made of how Peter Jackson had originally planed to split The Hobbit into two films and was asked by his studio to expand it into three parts. This necessitated scouring the Tolkien oeuvre for more material to adapt, writing new scenes, and bringing the actors back to film said scenes. Even had the actors and Jackson himself not been vocal about which material had been added into the film as envisioned, it would be obvious to most of the audience. The sad fact is that the added material sticks out like a sore thumb and it distracts away from the brunt of the film.
Understand this - The Desolation of Smaug is enjoyable to watch. That does not mean that it is a good movie. A good story has a definitive beginning, middle and an end. Even if it is part of a larger story, that should hold true. In Smaug's case, it doesn't. The opening flashback scene in Bree feels tacked on and unnecessary. The ending comes in the middle of what should be the climax. The love triangle seems particularly pointless. And Legolas the parkouring ninja is just annoying.
Yet all of these scenes are worth suffering through for the great moments. The dwarves' escape from Mirkwood. Gandalf confronting The Necromancer. And every damn scene between Bilbo and Smaug. If you enjoyed the first movie, you'll probably enjoy this one as well, though there will be points where you'll be shaking your head and wondering if certain things were really needed.