I saw it in 48 FPS. Here are my spoiler-free thoughts:
When it came to the fully-CGI aspects of the film, especially CGI characters and creatures, it was excellent. They felt really alive and authentic. We're used to this from video game cutscenes and the like, though. I think a fully-CGI film will look absolutely great in 48 FPS.
Conversely, when it came to scenes with live actors, it often looked too real. Like a bunch of LARPers with bad makeup putting on a play. This might have been fine with a story more grounded in reality, but my girlfriend and I felt it detracted from the mythic/fantasy illusion they were going for. It got a bit better later on. We want to see it again in 24 FPS and see if that restores the illusion.
Then again, the 3D did look a lot more convincing in 48 FPS than most 24 FPS films do.
On the other hand, when the camera moved very quickly, especially during action scenes, it almost gave me nausea. With static shots or slow pans it was fine. But if the side benefit of this is the death of shaky-cam, consider me an instant convert.
I'm not dismissive of the format as a whole, and I think it will definitely improve over time, but, like Bob, I feel filmmakers will have to do a lot of reinventing of their craft. Not just camera placement, but lighting, editing techniques, new types of makeup, and so on. And I'm not sure having a fantasy film being the first test of the format was the wisest decision, but as my friend said, someone had to be first.