Spoilers ahead, so beware if you haven't seen it yet...
I loved revisiting this universe. From the opening showing the dwarves at the height of their power, to hints of Smaug, to Hobbiton, Gandalf, Frodo(!), and the elves, it was great to be back. I especially enjoyed all the musical cues. All the themes Howard Shore used in the Lord of the Rings saga came back here, along with new music for the dwarves at Erebor and The Company. I grinned with sheer joy whenever I heard a musical cue for the elves, the eagles or the Hobbits theme.
I knew it was going to be a long movie with far more material than we needed, like Radagast, the backstory with Azog the Pale Orc, hints about the Necromancer, and so on. I don't care. I didn't mind that extra footage at all, and in fact actually enjoyed it. The 3D was better than I expected, but it didn't add that much to the movie. I started to get a headache near the end, but I may have been sitting too close (2nd row from the center aisle). I'll sit further back the next time I see it. Also, I saw it in regular 24FPS 3D, not the 48FPS version that some have said looks too real. What I saw looked good enough to me. I'd be fine with a 2D version, in fact.
Peter Jackson made these movies for LOTR fans, and as a huge LOTR fan I have a well-established bias. If you loved the first trilogy then I think you're going to enjoy this movie. If you didn't see the original trilogy or were bored, The Hobbit isn't going to change your opinion.