I guess I can answer this in two ways?
I mean, the first is just totally subjective in the sense that it really immerses you in the performances. I saw it on opening night projected in 70mm in NYC and it was really really cool looking. It was almost the film version of "hi-def," I guess? You can see every bump and imperfection on each actor's face. There was really no room for shitty performances, or they would've been so, I don't know, obvious? If that makes any sense?
The other answer would be a technical one: traditionally, the 70mm format is used for big epics & landscapes. See also: Lawrence of Arabia. The film is very hard to find and very expensive/difficult to work with. So not only was it interesting on its own that he chose it for a modern film, but even more interesting that he didn't use it for those huge landscape shots. The close-ups in 70mm just seem so much more real and personal.