The last Justice League movie only featured roughly 20% of Snyder's footage, and the rest was re-written, re-shot, and re-edited by Joss Whedon in two months. And, well, it shows how poorly planned that was.
Now, not only are we only going to see 20% of the first film, but this version is going to be 4 hours long (and R-rated) with nothing but Snyder footage. So yeah, this is going to be a very different movie.