Justice League clocks in at exactly two hours, apparently mandated by Warner Bros. executives, and it's hugely to the movie's detriment.
While it's fair to argue that Batman v Superman was over-plotted and excessive, this is almost the complete opposite, a breezy, inconsequential sprint that's over before you know it.
Unfortunately, though, this means that Zack Snyder and Joss Whedon have to speed through so much exposition and character building that much of it doesn't even touch the sides. Getting the League together doesn't feel particularly earned, and countless scenes from the trailers have been cut, presumably in order to hit that demanded runtime.
It's a breathless film where scenes aren't really allowed to linger and most everything feels chopped up to run the bare minimum length possible. To say that the film would've benefited from an additional 15-20 minutes of room is undeniable.