My wife and I have been going back and forth with this film, and discussing where it fails. Here is a quick list of my thoughts:
The Good:
I love the characters in this film, for the most part. Thranduil and Thorin are among my favorites, and get some great moments in their respective kingdoms. I especially love when Thranduil talks to Bilbo, as well as Bilbo, Gandalf and Bard's reaction.
I thoroughly enjoyed the battle at Dol Guldur and Elrond's moment of absolute epic strength. Definitely interesting dynamic versus the usual sword against sword battle.
Finally, I thoroughly enjoyed the visuals of this film, especially Smaug. The burning of Lake Town is an incredible sight to be realized on screen, and carries a heavier weight that I think is accomplished quite well. The final battle between Azog and Thorin also works quite well, as Azog feels very real and in that moment there is a real menace to him.
The bad:
*sigh*
The focus of the film is all over the place. As interesting the characters are, the film focuses too much on Legolas and Tauriel, and their meandering adventures all over Gundubad, and Dale, and Ravenhill, that it takes the film down in its pacing. It distracts from the the plight of the Dwarves, and the introduction of Dain, as well as the aftermath of the battle.
The ending is frustrating because it just ends. Unlike ROTK, which goes on forever, BOT5A, just stops, with no resolution, and no sense of the impact on Bilbo. It relies too heavily on the viewer knowing the LOTR films to filll in those gaps.
The love triangle between Tauriel, Legolas and Fili is just, to be blunt, shoved in there for no reason. Tauriel's character takes her from skilled warrior to blubbering love-struck female who gives away a tactical position and nearly gets herself killed. The whole tone of the fight gets deflated in that moment.
There is a lot of wasted potential here, especially with the company of Dwarves who we get to know over AUJ and DOS only to be left in the shadows for the sake of unnecessary characters and moments. There is more, but I think that sums it up.