Michael Bay is in desperate need of an editor to cut about an hour of total crap from this movie. That would make the not awful parts a lot more tolerable, even if it still would be a largely incoherent pile of "stuff that might look cool" thrown together.
Way, way, WAY too long. It's bloated, padded, and make up any adjective you want with stuff that is only there to kill time. The whole end of the fight scene at the end of the movie makes no sense whatsoever. And why does Tauriel even exist, since the whole thing is cringe inducing once she's with Kili? Oh yeah, that was one of the parts Peter Jackson just pulled out of nowhere and made up because he really wanted to make a trilogy without enough source material to do it. Highly disappointing, I'm still not sure if 2.5 is too high.
As usual, Loki steals the show. When he's on screen, this movie is great. When they're on Asgard it's also great. Unfortunately, then they go to Earth and we get old guys without pants jokes, and some not very interesting bad guys in the Dark Elves. Also, once again, where the hell is SHIELD in all this?
That's the biggest flaw in these movies post-Avengers. After setting things up for what SHIELD is and what they can do, their absence in this and Iron Man 3 is extremely conspicuous.