Let me start by saying that I enjoyed this movie. I would recommend it to most people. But even while I was watching it, there were issues that I had with the film that I need to vent about.
The Hobbit doesn't quite reach the standard set before it by the LOTR films, all of which had excellent pacing. It even starts off with a misstep: including old Bilbo and Frodo in the opening. Although all the exposition is nice, and its cool to see things that the book only ever alluded to, old Bilbo and Frodo do nothing beyond letting the viewer know "oh, this is an LOTR movie, it's got Elijah Wood in it". The pacing is better after that, once the main quest gets underway. The initial interactions between Bilbo and the dwarves are excellent, the first part of the journey is great, the troll scene is good (could have been better, but good), I loved Radaghast, the warg chase is cool, Rivendell is great. The council between Elrond, Galadriel, Gandalf and Saruman is excellently written and may be my favorite scene in the entire movie. Then the dwarves leave Rivendell, and everything draaaaaags. Basically, there's too much action. The entire last half of the movie is action sequences, save for the riddle contest. I like action and action scenes a lot, but an important part of pacing is putting space between action sequences, enough that the audience has a chance to catch their breath. Instead, there's so much action that it gets boring. It felt like the writers were afraid that the first movie would be too boring, so they padded it with more action. If you cut out the Frodo parts, the stone giant battle, and shortened the goblin chase scene and the pine tree showdown with Azog, you could easily keep the movie under two and a half hours. It had no business being that long.
On another note, I could write an entire review about how the riddle contest was mishandled. It's one of my favorite parts of the book, because it felt like Bilbo was playing chess with the devil. The only time Gollum has ever achieved an air of menace was in the first LOTR movie, when you didn't see him. Once we saw him, he became something for us to pity. To do the riddle contest justice, it needed to be dark and it needed to not show Gollum very much. Instead, we got an extremely well-lit cave and Bilbo looking more baffled than frightened by this bald monkey in front of him.