I watched it this past weekend. I saw the HFR version, but this was actually the first 3D movie I'd ever seen so I can't say how it compared to other 3D formats or to other 3D movies. From some of the things I'd heard, I was half expecting to get a headache or feel nauseous or something. But it had no physical affect on me at all. I'm not normally susceptible to motion sickness though, and I rarely get headaches.
The 3D looked pretty cool at first, but within a few minutes I almost forgot I was watching 3D. Actually, I think I'd stopped noticing it by the time the 3D movie previews were over with. I could see the effects when I thought about it, and it did look nice, but the effects weren't as in-your-face as I expected. The only exception was when the occasional flying object came toward the camera, which made me flinch and remember I was watching 3D.
I really liked the movie itself. I wasn't bored and I didn't look at my watch at all. For me, the three hours went surprisingly fast. As much as I love the LOTR movies (and I do still like them more than this first Hobbit movie), I usually have to watch the extended version of each movie over the course of two days, because that's just too much time for me to spend watching the TV in a single day.
I thought there was a good mix of action and dialogue/plot development. I like action, but I get bored with it fast if it's just a long, drawn-out battle scene or something that doesn't really move the story forward. Especially when everything's moving so fast that it's hard to tell exactly what's happening. There was a little bit of that in the movie, but not so much that it got boring. And the more meaty sequences made up for it.