I've seen The Hobbit in 3D HFR, 3D IMAX HFR, and plain old 2D 24fps, in that order. Note that I don't have stereo vision, so the 3D part doesn't impact my experience, other than the 3D versions are darker (not really an issue in a darkened theater IMO).
I really, really wanted to like HFR. I went in all gung-ho, looking forward to embrace a smoother future. 48fps took a while to get used to. But even after I got used to it, it looked worse. It's like watching BBC's Life documentary with pasted on hobbits and dwarves in costumes. Just like HDTV brings out flaws in make-up, 48fps makes animation flaws much more visible. As there is a LOT of CGI in the movie, such scenes look even more CGI than they do in 24fps. Somehow also the live action scenes look like they're happening on a sound stage more than they do in plain old 24fps. 48fps breaks the fourth wall, and it's never mended. At least it didn't for me in two viewings.
As an aside, Peter Jackson uses extensive frame rate manipulation: many action scenes are shot in slow motion. I actually thought this was my brain playing tricks on me until I saw the 24fps version and confirmed to myself there are slomo sections.
I sincerely hope that 48fps will take over some day, but not in its current incarnation. My layman but movie buff proposal is variable frame rate: use 24fps where it works, but switch to higher fps for panning shots and otherwise difficult shots which don't really work in 24fps.
To close off, I'm going to see The Hobbit at least once more in the theater, in 24fps and perhaps one more in 48fps. It's a stunningly beautiful movie not only visuall, but aurally as well as story-wise, and PJ has (re)created a rich world that I recognize from the books and LotR movies.