I will cheat here and include the Forbes Review, which I liked
http://www.forbes.com/sites/erikkain/2012/12/14/the-hobbit-an-unexpected-journey-review-the-best-middle-earth-movie-since-fellowship-of-the-ring/ Now for my take. Big spoilers so enter at your own risk.
Martin Freeman was brilliant. It makes all four hobbits in the first film seem amatureish, but of course Jackson has evolved as a writer and director. (and I never did care for his total screw up of Merry and Pippin anyway). The Gandalf we see is quite like the Gandalf in the Hobbit-- more fun, less certain of himself as he is in LoTR. All of the elements the Forbes review describes are there in the Hobbit by the way, regarding Thorin and his hubris but we tend to dismiss it because it's a "children's book." I am rereading the Hobbit and see all the plot points Jackson brings up which I have overlooked in each time I have reread the book.
The casting of the dwarves is wonderful. They are not cartoon dwarves, they become real and all the more tragic since we know who lives and who dies. Richard Armitage is in fact a combination of Aragorn and Boromir and I noticed that right away. The "bend the knives and break the plates" scene is great.
The scene of Erebor and Dale before the coming of the dragon is great. Jackson devices pre industrial age methods for minin and show show us the dwarf kingdon and how they mine and process gems and gold. I swear he got one idea from Cowboys and Aliens.
Bilbo's motivation for going against the trolls is different in the book -- the trolls have stolen some of their ponies to eat including Bilbo's mare named Myrtle. And by damn he's gonna get her back! And he plays a larger role in the demise of the trolls by buying time for Gandalf as the sun rises. This is lost on Thorin who has to be reminded by Gandalf.
We see Rivendell through Bilbo's eyes as they are leaving to continue their quest . We know Bilbo always yearned to go back there so this becomes more meaningful since we know eventually he does.
By the way, Thorin and Co are hunted by orcs and wargs prior to getting to Rivendell and that's pretty spine chilling. Watch out for Radagast and the Bunny Sled. The only jarring thing about Radagast is the bird do do running down his face. But he's a cool character and more enaged in the goings on of Middle Earth than Tolkien ever gave him credit for. There is a wonderful scene where the dwarves ask Gandalf are there any other wizards and he runs through the known list, but can't remember the names of two of them, because of course, Tolkien gave us 5 wizards but only named 3.
The Riddles in the Dark scene with two mature, brilliant actors was spine tingling. We see just how low Gollum has sunk. And the way the Ring winds up on Bilbo's finger is resonent of the way it winds up on Frodo's finger at the Prancing Pony. We see the world the same way by the way, when Bilbo is "invisible" -- that hazy, shadowy ghost world.
That moment when Bilbo spares Gollum is wonderful. Pity stirs the hobbit's heart for this wretched vile creature. Again, two mature actors in a pivitol scene.
There are some gags I didn't care. We see the elves more through eyes of the dwarves and the hobbit. Elves apparantly live on salad by the way so if you're on a diet, Rivendell is the place to be. Elrond is more "fun" like Gandalf" although he is out of character riding back into Rivendell having been orc hunting. Part of the deal when you become a great healer is that you give up fighting, which is why Elrond never took up arms the way his sons did (I am the Tolkien geek, recall).
And I'm not into troll snot. Or cutting up the furniture in Rivendell to fry sausages.
The White council meeting is interesting. Saruman is a total buzzkill clearly trying to distract Gandalf, who can't quite explain himself. Galadriel is obviously on to Saruman who just becomes background noise while she and Gandalf communicate telepathically.
The bit with the stone giants in the Misty Mountains is gripping. Goblin Town is a little disneyish -- I can see a ride coming out of this-- but overall entertaining. The great goblin though was way too - well he looked like one of the Bosses on Naboo who arrest Jar jar Binks frankly. so he's a little hard to take seriously.
After the escape fro the mountains and Bilbo becomes visible to the dwarves, they ask him why he came back because they have thought he has left them. He says, "I have a home. I miss it. But you don't have a home. I will help you get yours back if I can. That's why I came back."
Did I mention Martin Freeman was brilliant?
After that we have the bit with the 15 birds in 5 fir trees and that will have you on the edge of your seat. There is a major bad guy reimagined for the movies -- Azog the orc who is dead in the books, but very much alive in the movie and gunning for Thorin as Thorin is gunning for him. He looks more human and less orc so we take him very very seriously. Trapped in the trees with fire all around, thinking he's gonna go down, Thorin takes on Azog only to get munched by Azog's ginorous white warg. Bilbo leaps down to defend Thorin and the other dwarves follow. Here come the Eagles! They deposit the lot on the Carrock which is a HUGE ass rock from which they can see Erebor. Thorin embraces Bilbo and says all his prior negative opinion of him is erased, he DOES belong with the company Bilbo says, "Well the worst is behind us." Whch we know is horseshit. Then we fly to Erebor over the desolation of Smaug through the eyes of a thrush. And we see the eye of Smaug opening. Cue credits.
Oh and Martin Freeman is brilliant.