We'll never see what Zack Snyder's fully realized DC Universe would have looked like, but the man himself promises it would have been amazing. In a recent social media post the Batman v Superman: Dawn of Justice director was asked if we would ever have seen a Flashpoint storyline in the DC film universe if things had gone as Snyder originally envisioned. In response, Snyder left a single word, "better."
Exactly where the current DC film universe is going as a cohesive world is far from clear but the one thing that does seem to be accurate is that Zack Snyder will not be at the helm. While Snyder is still technically a producer of the franchise, he left Justice League before reshoots were completed and his focus as a director now seems to be on an adaptation of The Fountainhead rather than anything involving comic book superheroes. Snyder says that he learned of Affleck's decision to leave the role of Batman when everybody else did, which would seem to confirm he's not directly involved in the franchise anymore.
Originally, Justice League was announced as being a two-part movie but that idea got squashed into a single film. How much of what Justice League turned out to be was the work of Snyder as opposed to Joss Whedon, who came in to handle reshoots, has been a topic of contention ever since.
Justice League largely floundered at the box office, but many vocal fans believe that if Snyder had been able to complete the movie himself a far superior film would have resulted.
Snyder doesn't elaborate at all on what he means, but you can bet that fans all sort of had their minds blown at the idea. What exactly was Zack Snyder's grand plan for the DC heroes? He calls Ben Affleck the Best Batman Ever in his post, so one can certainly guess that Affleck leaving the role right now was certainly not part of Snyder's road map. Certainly, a great deal of material was lost when Justice League became a single film, but we still have little idea what would have been in that longer story or where it would have pointed afterward.