The Desolation of Smaug is a perfectly serviceable, better than average, action-adventure fantasy–assuming that you have seen the first movie and don’t mind that the second ends in a cliffhanger. Still I feel a bit disappointed. This doesn’t seem nearly as good as Jackson’s adaptation of the Lord of the Rings.
The movie is fine from a technical standpoint and the actors are quite up to the material. The problem is with the writing, and here I feel that Jackson’s decision to expand the novel into a trilogy-length story is not working out well. Tolkien, whatever you may say about his limitations, was a master storyteller. The screenwriters are not on the same level. Most of what they have added is routine Hollywood hackery. Even if you haven’t read the book you could probably write the script for the third movie yourself given what they have telegraphed in the second.
Not everything they have added is bad. Introducing Legolas (Orlando Bloom) when the party enters Mirkwood makes sense. Based on what we know from The Lord of the Rings he belongs there. (It makes sense from a commercial standpoint too of course.)
And Legolas is assisted by a spunky Elf maiden (Evangeline Lilly). There are few stories that couldn’t be improved by the addition of a spunky Elf maiden.
On the other hand there are some small changes, made purely for dramatic effect, that I found annoying. I can say with confidence that Tolkien had a much better understanding of the phases of the moon and the floatation properties of barrels than Jackson does.
As for the main addition, Gandalf’s battle against the Necromancer, it ends up with Gandalf (Ian McKellen) looking pretty stupid. Gandalf is supposed to be smart, but there is no sign of it here. He’s acting like a typical Hollywood hero with lots of courage and no brains.
Still as I said, as popcorn entertainment this is fine, better than average even. Just try to avoid comparing it to the original.