the use of shadows was done to cover up the fact that Brando was fat, Martin Sheen almost died from a heart attack, and filming the movie is said to have driven Coppola mad, and that's some of the stuff. There's a whole doc on the making of this film.
As for remaking it, I mean any war movie can utilize the same themes discussed in this one but like Ziggiy said, the bts craziness can't be duplicated, the level of acting more than likely won't be up to par, very few directors are and can reach the level FFC was at in the 70's, and in general, the Vietnam War seems to be a better backdrop for films than the Middle Eastern wars have been.