First thoughts. This looks a lot more like LotR than Unexpected Journey did. Radagast did not make a single appearance. The Thranduil plot divergence shows some promise of being exciting/interesting. Smaug sounds a little like The Eye (Thief: the Dark Project). The Gandalf/Radagast storyline is really at odds with Gandalf's ignorance of Sauron in LotR.
Further reflection on the above...Unexpected Journey diverged sharply from LotR character and creature appearance/clothing/etc. while still trying very hard to root itself in it (adding characters who really didn't further the storyline because they were popular in LotR, etc.). Based on what the trailer reveals, it is reasonable, I think, to speculate that they perhaps recognized this as a short coming. This just looks and feels more like LotR. As to how much could be corrected (the filming was all but done), that remains to be seen; at least in the trailer, however, they didn't embrace the divergences from the prior trilogy. Likewise for the absurdities.
Which is a perfect lead-in for Radagast the Brown, who made a complete non-showing in this trailer. Considering that he was a character of considerable consequence (and controversy), this seems significant; could it be that the studio realized that Radagast was a hideously unpopular character, and so decided no to remind fans of him while enticing them to watch the second film? Probably. On the other hand, while it's too much to hope that Radagast might take a shower/fall in a puddle/glance in a mirror and realize “Oh my god! There's fecal matter running down my face; I'd better get this off or I'm going to die of some nasty disease!” is it too much to hope that Peter Jackson will tone down the stupidity overload that has become the brown wizard? Again, probably. As it is, we're stuck with the aforementioned bird & fecal-matter headdress, the bunny-drawn sleigh, etc. Based on the leaked images of Sonic the Werebear...I'm sorry, Beorn...it doesn't look like absurdity is going anywhere soon. And based on the Goblin King (or, as How it Should Have Ended put it, he of the “scrotum beard!”), Jackson has a significant penchant for silliness. However, if you're an ardent fan desperately searching for a glimmer of hope that Peter Jackson recognizes that viewers aren't keen on the, shall we say, extra-creative touches, consider extrapolating said hope (though it probably isn't justified) from the fact that absurdities were kept to an absolute minimum in this trailer (and then in all likelihood be disappointed come December). That's my plan. ;)
As for Thranduil...he seems to be shaping up as a genuinely interesting (and sinister) character. Obviously different than the book, but different in a promising way. It remains to be seen how it is done, of course, but my curiosity is piqued.
“Well, thiefff...” Khan as Smaug. Awesome. Also reminiscent of Thief I's “the Eye”. A trifecta of awesome.
And, finally, as for Gandalf's continued realization that Sauron is at work in the world...it seems very much at odds with the entire beginning of The Fellowship. It will be interesting to see if Peter Jackson accounts for this in any way.
These are my initial thoughts after watching the trailer. Of course, I'm going to watch it when it comes out. (It's The Hobbit, for heaven's sakes. How could I not??) I think it's clear that this is not a production of the same quality as The Fellowship or Two Towers, or even Return of the King. But, if this trailer is any indication, it promises to have its moments of magnificence. I am moderately optimistic.