I just came home from watching it twice. It premiered here a few days back and first I saw it in 2D and then in 3D - I can highly recommend the 3D version if you have the coin, it was by far the most engrossing version. And I'm a guy who abhors 3D normally.
Now, I'm going to give a thorough opinion on all aspects so expect spoilers below. I dont want a whole post marred by black bars so just dont read further if you dont want things spoiled.
The Acting
I'll begin with the thing that most impressed me, the acting was superb by all accounts. I love Lee Pace as Thranduil and he certainly exudes the wildness I expected. Everybody did a great job - Martin Freeman could express more with his body and facial language than most can reading Shakespeare. The CGI was a bit heavy on some characters but even then, Billy Connolly as Dain and Manu Bennett as Azog were great.
One of the scenes that got me teary (both times) was the scene with Tauriel, Thranduil and Kili. Wow man - I know a love triangle drama seems a bit off but Evangeline Lilly impressed me so much. I was really moved.
The Music
This was a bit on and off. Sometimes, the music hit great notes, for example when Bard is aiming for Smaug, but other times... I can say it was satisfactory but I sort of expected much more from the last chapter of the trilogy, music wise.
The Story
This is both good and bad. Thorins arc and the small touches with Saurons plan and banishment were nice, I liked it. It tells us a great deal about the motivations and machinations of some of the bigger players in LotR. I personally felt enlightened. But... yeah, a lot of things I didnt like. Like, why was Smaug killed in the first 10 minutes? I know the dragon dies but seriously, it dies so quickly that it SHOULD have been done with in the second movie.
Another thing was why Alfrid was given so much screen time. I mean seriously, any competent director needs to ask himself (for every single scene); "What does this scene show and do I want to tell the audience that ." And I've seen the movie twice and I find no good reason, or any reason, why Alfrid needs a single iota of screen time. The ONE thing he does at the end is, he gives exposition time to Bard; "Oh you could have been king, why give it up? For family!?" - I mean thats it. They spend so much time on the dude all so he can show us that Bard cares more about family than gold. But it was unnecessary! Luke Evans does a great job of conveying his love and a lot of his scenes ARE about his family. We get it, he's a good man, we dont need Alfrid to tell us that.
If you argue that he's supposed to be the comedic role - then he failed at that too. During both my viewings, the cinema laughed more at Martin Freemans shenanigans than anything the Wormtongue-wannabe did. Just a poor, poor choice.
Otherwise, the ending felt a bit... hollow. You're never told what happens with Tauriel or Bard or the surviving dwarves - I mean, some of it you would know if you read the book but any movie relying on outside sources to tell its story is failing as a movie. I'd have rather have the "multiple endings" of RotK than an ending that doesnt seem complete.
The Action
The action was very cool. Just looking at the broad battle strokes, I liked the ebb and flow of battle, it felt very real. Going on the offensive, going on the defensive; to me it felt more like "real" battle where things are ever changing based on strategic moves.
As for the individual action, I also liked a lot of it - barring such craziness as Azog jumping out through ice. I mean, I dont care how strong he is, you cant do that unless you got a jetpack strapped to your back. The fighting was clean, visible and very well choreographed. Especially the scenes like the dwarven shield wall and lance attacks, so cool.
Overall... hmm... I'd say it's a decent movie. I liked it. I was hoping for a bit more - as it is the closing movie - but it's decent. I can recommend that you go watch it if you've been following the series.