For those interested in a long technical read, here's an interview with Lee about the technology behind shooting in 120fps 4K 3D:
Ang Lee On His Game-Changing ‘Billy Lynn’s Long Halftime Walk’
The abridged "Too long, didn't read" version:
The increase in detail is so ridiculous that Lee says you can't calculate it, it's its own thing. The reason he went for 120fps is because it would be easier and cheaper to convert to both 60fps as well as the traditional 24fps framerate (because 120 can be divided by both 60 and 24).
According to Lee they had to give up on using any make-up on actors because the quality is so high you could see the make-up. They had to completely rework sets and how to shoot scenes because the quality is so high you could tell it's a set. The picture quality requires so much extra lighting that it became a problem to fit enough lights into the sets, plus every single light source both off but especially on screen had to be selected carefully because even the most minimal of flickering would be visible and distract.
Lee also said only a handful of theaters will be properly equipped to show the "Whole She Bang", which is the 120fps 4K 3D version. He says that most theaters will probably show the movie in either 60fps 3D or 120fps 2D in 2K.