Having seen the first installment of Peter Jackson's Hobbit trilogy, An Unexpected Journey, twice now, once in 24 fps, and once in 48 fps, I've been able to compare the merits of both in pretty close proximity to each other.
Despite all the negative reactions swirling around the High Frame Rate release, I was blown away by it. Granted it does take some getting used to, because your eyes are being asked to absorb twice as much information as they're used to, filling in many of the visual gaps that our eyes are used to filling in on their own. It's almost like watching a silent film being projected at the wrong speed, everything seems to be moving too fast. But once you get acclimated to it the effect is spectacular. Everything looks so clear, almost hyper-real, making for some of the most breathtaking 3D ever.
I think many people passed judgement on it too quickly, decided they didn't like it right off the bat. Because it is a bit jarring at first because it's so different that what we're used to. However I think if people give it a chance it makes for a wholly new and thrilling cinematic experience.
The 24 fps looks great too, of course, and has a more traditional film-like quality that is more reminiscent of the look of the Lord of the Rings films. But the 3D conversion isn't as good. The 3D effect is much sharper and more real in 48 fps.
The bottom line is that the movie is great no matter what format you see it in. You can read my full review of the film here (which is based on the 24 fps version, I had not yet seen it in 48 at press time). But the HFR version is just such a unique experience that it's something that should be seen, if for no other reason than just to take in the breathtaking detail that Peter Jackson has poured into the film. It really comes to life in 48, and deserves to be seen the way the director intended.