Saw it today in the HFR 3D.
It was .... OK. I didn't suffer any ill-effects from the 3D. I'm not sure that the 3D effect added a great deal to the experience for me, though. There were a few highlights, like the birds, but on the whole I prefer the cinematic look of the LOTR trilogy. The 2D version seems to have been slightly compromised in places by the demands of HFR, which is a shame.
Some sequences I found were really naff in 3D, it was like looking at cardboard cut-outs against a painted backdrop.
I was particularly disappointed with Rivendell, both in the 2D and 3D versions. In LOTR, we know it was a miniature model, but my god, it looked so breathtaking and real. In this latest film it looks like a rather crap painted backcloth. I was hoping that it would look better in the 3D showing, but it didn't. (Lovely to see Figwit again though!
Still enjoyed the film a lot. Just great to have more of Middle Earth.