The Hobbit, in IMAX, was fantastic. Drain all bladders before taking your seat: there is something like 166 minutes of film, preceded by 30 minutes or more of trailer, ads, and the usually turgid mush about the mind-splittingly good technology that is going to make your experience unparalleled.
Before we get into a brief description of the thing, I'd like to note that the Hobbit probably represents the only new estate in big budget blockbusters - all the trailers here were for reboots: Superman (again), Wizard of Oz (a sequel), Star Trek (OMFG again).
This Hobbit screening was not only IMAX, it was 3D, which is generally of gimmicky quality. This, however, was very good - I couldn't suppress a flinch at an incoming spear during the Star Trek trailer, and there were times when it appeared you were looking through a hole in the wall of the cinema rather than at a screen. No doubt, the 48fps had something to do with this. Pan shots were very smooth and there definitely was a parallax-scrolling effect going on during the wide travel shots.
Top tips: Do not sit near the front. You will be too close to the screen and you won't be able to see the edges. Do not move your head around, the 3D effect appears to be delicate and even a moderate tilt will blur out parts of the picture. Do not bring excessively small humans, they have tiny internal waste storage spaces and may cause you to miss chunks of the movie when they need emptying. Do not bring a picky perfect recall of the book, loads of original material has been packed in to make a solid movie from what is really a short book constructed for the appreciation of young readers.
About twenty minutes from the end, the sound and picture streams de-synched at our showing, but by giving us free IMAX tickets for another show, the management of the cinema forestalled the impending torches and pitchforks mob.
Take the top tips above and go see it.