The movie begins with the much-anticipated attack on Lake-town. I have gone back and forth on whether or not this scene would have been better served as the climax of the second film (my brother's first comment walking out of the theater was that is should have been). This scene was always going to be tricky, because it is the very definition of an anti-climax. So framing it as a finale or opening was always going to be a disadvantage. Obviously, if you end DoS with Smaug's death and Lake-town's destruction, you run the risk of audiences being left confused as to what could possibly be left to cover yet another film (a problem that still exists). So baiting people with DoS's cliffhanger ending makes sense given the three-film split. It was a safer gamble to assume that people would come back to see what happens with Smaug and Lake-town, and then you can simply go from there.
But again, the scene is an anticlimax, and opening a movie with it still leaves you with a bit of a disconnect. You're starting the movie with what is essentially the conclusion to the previous film's final arc a year after the fact. The fact that it comes and goes so quickly only aggravates the jarring effect.
Tauriel, the dwarves, and Bard's children (with the exception of Bain) are given nothing to do but paddle through the canals as they attempt to escape. Bare in mind that the only reason they were kept there in the first place was to further the contrived "dwelf" romance between Tauriel and Kili, and to stuff in another action scene at the tail-end of DoS (which only served to detract from the main plot with Bilbo). Seeing as how their involvement in Lake-town was essentially concluded in DoS in that regard, their presence in this opening scene doesn't amount to much of anything. They are just there.
I am happy that the windlance never came into play here. Whether Jackson completely forgot about it (which wouldn't surprise me), or Smaug destroyed it and I just didn't notice, rest assured that Bard does attempt to take the dragon down with his longbow. From an action point-of-view, I have no serious gripes with this scene initially. Nothing was too over-the-top or physics-defying. And there are some great POV shots of Smaug circling Lake-town like a bird of prey (the one from inside Bard's prison cell is delightfully eerie).
What I ultimately did end up having a problem with is how Bard takes Smaug down. He has one arrow left, but his bow is broken. Fortunately, Bain is able to reach him with the Black Lance (Sorry, Jackson. That is not an arrow). With the windlance out of the equation, Bard crafts a makeshift bow, using his son's shoulder as a means of balancing the lance. Why Jackson had to overcomplicate this, I do not understand. Apparently, a bowman taking down a fire-breathing dragon with bow and arrow alone isn't "epic" enough. This is the "cooler" alternative, apparently.
This scene also rounds out an issue I had with DoS. Bain tells the dwarves the story of how Girion had wounded the dragon during its attack on Dale, leaving a vulnerable chink in its armor. Whether anyone chooses to believe this or not (the dwarves don't), the precedent is set for Smaug to possibly have such a wound. Bilbo obviously goes on to discover that this is true. And during his last stand with Smaug in Lake-town, Bard notices it too.
Here's the issue. In the book, Bilbo is the first one to discover the dragon's weak spot. When he mentions this to the dwarves after-the-fact, the thrush sitting by overhears him. When Smaug attacks Lake-town, the thrush arrives and passes this information onto Bard (who can understand the thrush due to his ancestry). This is important for two reasons. One, it makes Bilbo a vital part of Bard's victory. Without Bilbo discovering that wound, it is likely that Bard would have been dead long before he would have found it for himself. Bard does not kill that dragon without Bilbo's help. Two, the involvement of the thrush is thematically significant to further highlight the importance of Bilbo's connection to nature in contrast to the dwarves' connection to materialism/industrialism. Nature vs materialism/industrialism is an ever-present theme throughout Tolkien's text, and this is especially true in The Hobbit.
In the film, Bilbo's involvement in Smaug's destruction is entirely non-existent. Once again, his role is minimized in favor of a secondary-turned-primary character. This is made worse by the fact that Jackson cuts away from Lake-town from time to time to show Bilbo and the dwarves watching the town's destruction from afar. In the book, Bilbo is indirectly responsible for Smaug's death. Here, he stands and watches helplessly.
The attack on Lake-town should be horrifying, which it is at times. But the effect is diminished by Jackson's penchant for forcing in comedic beats that only serve to confuse the tone of the scene. This scene should not be pretty. People are dying, their homes are being destroyed, and there is seemingly no escape from this unstoppable creature.
So when you keep cutting to the Master and Alfrid desperately trying to escape with a boat over-filled with gold, only to have the Master die from Smaug's body crushing him and his boat, it all comes across as poorly-timed and inappropriate.
Right from the start of the film, you get a sense that the excessive amount of CGI was going to be a problem in certain areas. Smaug himself was fine, but the CG Fire was pathetic, both by Weta and 2014 standards. At times, it looked and behaved more like orange smoke than living, tangible flames. It almost looked like something that you'd see from a video game console.
As a result, the tangibility and visceral feel of the destruction is diminished by the sheer artificiality of everything. It undermines the physical horror in a very disappointing way. It's too clean.