So let's get this out of the way first: this movie is bad. I mean, it's bad. And not in the way that most superhero movies are bad, though it is bad in that way too: inconsistent characterizations, lack of understanding of motivations, weirdly-shot fight scenes, dodgy use of CG, etc. I mean, it is bad in all of these ways too, especially the whole thing where they digitally removed a mustache from Henry Cavill, who's honestly doing his best with a bad script and a character he's fundamentally unsuited to play. Gail Godot, in an iconic roll for her, suddenly shoved out of the way to make room for (also fundamentally-miscast) Ben Affleck's the Batman and Cavill's Superman, And Ray Fisher and Ezra Miller trying to introduce characters that honestly deserve their own movies. Jason Momoa's Aquaman got his own movie, but as far as I can tell he's just stepped into this one from a whole different universe and is basically pretending to live in the grim-n-gritty DC Movie Universe so he can get a paycheck, and consequently he feels even more disconnected than Wonder Woman, which is a feat.
The problem with Justice League, well, one of the problems anyway, is that it's trying very hard to tell several different stories, each of which would probably be doable if they had their own movie to tell, but that would mean actually committing to the Marvel-style methodology of "what if we made a miniseries but filmed them like movies so we could sell more tickets", which Warner Bros. seems absolutely incapable of doing. What that means for the movie is the biggest problem I have with it, which is no one does anything for a reason other than "the movie requires them to make this decision to move the movie forward". It doesn't help that the Superman and Batman movies that were designed to lead up into Justice League were just as terrible as this one, but with less excuse. So now we have an overstuffed mess of a movie that's got a 2-hour runtime that feels like more where no one is motivated by anything but plot. There's a scene in this movie where the good guys have possession of the mcguffin and then leave it on the roof of a smashed car so that the bad guy can grab it. That's not me being hyperbolic; that's an actual, honest to gods plot point. "How does Steppenwolf take possession of the third Motherbox? He grabs it off the street while the heroes are fighting each other."
This could, in theory, be considered a spoiler, by the way, except that the trailers for the movie gave away this particular plot twist before it actually made it to the theaters, and also there's no reason for this to happen so even revealing this plot point doesn't actually tell you anything. There are lines in the movie that don't make any sense at all. Like, not just "why would someone say that in this moment" but really, actually "that sentence made no sense at all, even if it wasn't Superman saying it". To quote a very good movie: "This episode was badly written!"
I am not the biggest fan of superhero movies anyway, because I think often they ignore what's interesting about the characters or the ideas in order to show off someone's special effects budget, but I will admit that I have a particular loathing for the DCMU in it's utterly baffling attempt to "make supers for Grownups" by completely failing to understand both superheroes and grownups. There are some good supers movies; the best ones are the ones that lean into the comic history of these characters. Most of them are merely OK because they decide the important part is the flash over substance. And the worst are the movies that think they know what's best about superheroes, and miss.
So if you're looking to waste 2 hours of your time, almost anything would be a better choice than this movie.