I saw it Saturday in 3D Imax HFR (at least I think I did- the theater I went to was listed as having HFR capability). I did notice that the 3D previews that were presumably not shot in HFR were harder on my eyes.
I didn't have any trouble with the movie itself, except for some of the really fast action sequences being hard to follow. We got there early and got prime seats, so that may have helped. This was my first 3D movie, and I didn't get a headache or anything.
On the whole I loved the movie. The only continually jarring thing for me was the actor who played Kili. Having seen the first season of "Being Human" where he plays a vampire, I had trouble adjusting to him in the role of Kili. He just didn't get enough lines to make him "Kili" in my mind. So, every time I saw his face, it was a muted sort of
reaction on my part, and his role as Mitchell would come to mind.
I didn't have that problem with Martin Freeman at all. I loved him in Sherlock, but he instantly turned into Bilbo for me after just a few minutes.
As usual, I couldn't see the reason for some of the changes from the book- they didn't seem to be time savers and thus.... what's the point? When the book was quoted word for word, though, I just sat there grinning.
I liked it.