I went to see The Hobbit: Desolation of Smaug yesterday. I don't have all that much to add to what everyone else says, and the most obvious problem with the movie is precisely what everyone says it is -- the pacing is completely off. We keep lingering on side issues and speeding through essentials.
I think a great deal of the problem is that Jackson has sliced the movies badly, plus let too much filler be added to the script. If you really had to make a movie for The-Hobbit-plus-background-to-LOTR, the second movie should really have involved two things: the dwarves making their way to Smaug and the Council of the Wise assaulting Dol Guldur. We barely got anything related to the latter here, which means that the third movie is going to have to see the death of Smaug, the assault on Dol Guldur, the Battle of the Five Armies, and everyone getting home, which is far too much even for three hours -- something is going to get shortchanged. And, frankly, from the all the made-up action sequences here, it's quite clear that something like the assault on Dol Guldur was needed here. It would also have been able to take care of a lot of what the filler was thrown in for. Need a strong female character? Have Galadriel direct troops in person. Need spectacular special effects? Let's see Saruman's magnificent assault weapons. And it would have been more faithful -- Galadriel might well have been there in person, and LOTR explicitly tells us that Saruman's machinery was a major part of the assault.
The filler is also getting to be a bit much. I don't have much of a problem with modification for cinema, but it's a problem when the filler is starting to choke out the original -- it begins looking like bad fan fiction. The filler needs justification. It makes sense that we would get more Legolas here than in the book, since he would have been there doing something anyway, and the movie is a prequel to the Lord of the Rings trilogy; it's reasonable to set things up, then, for the Legolas-Gimli interaction. Tauriel, on her own, is a not-unreasonable kind of character. But the Legolas set-up is a secondary matter, and invented characters should either simplify the story (e.g., by summing up what would otherwise require several characters or complex scenes) or add nice touches, not require their own entirely fabricated storylines. We spend a ridiculous amount of time on Tauriel here, and we already have the Azog filler spilling over from the first movie. We aren't just dealing with added storylines here; we're being subjected to major divergences at significant points, since they are starting to interfere with the main story.
Other weaknesses: Smaug is too talky -- yes, he's a vain dragon, but he just never shuts up. We never get any sense of why the Master celebrates the dwarves, perhaps because the reason is that he wants to get them out of town as fast as he can and the script leaves a third of them in town for no good reason. Almost the entire Lake-town portion is botched, in fact. We don't get enough of the mirkiness of Mirkwood.
The strengths: Martin Freeman is such a good Bilbo Baggins that he deserves a better Hobbit movie. In fact virtually all the acting is quite good, even for the made-up characters. Despite an endless number of liberties being taken, the barrel sequence was done well (it helped that the liberties taken actually make some sense in terms of cinematic structure, since it made sense to have a bit more action at that point, and that it was done with a sort of zany zest without any pretentiousness, and that it was better done than the mountain sequence in the previous movie). I liked seeing the dwarven forges, which are the single best scenic part of the movies so far. Many of the smaller touches of the movie are just splendid -- it baffles me how so much obvious love and care can be lavished on little details when the seams of the main story are so sloppily stitched together, but the detail-work is often excellent, whether it's Beorn's bees, Gloin's portrait of Gimli, Bilbo's first introduction to the treasure under the mountain, or the scenery in Esgaroth which manages to tell us more about what's really going on than the script does.