I don't really know where to start with Justice League. It's not completely hopeless?
The was always going to be a messy film, a last minute director change, extensive reshoots, etc. But wow is it messy. It doesn't have pacing, at all, there's absolutely no sense of an act structure to the thing. The entire thing feels like it's in a rush to be over. In turn it seems to have no confidence in itself, it doesn't allow any scenes to breathe or have impact, preferring instead to smash through to the next seem less anyone notice it. I didn't think it was possible, but this might be first nervous movie I've seen.
The plot concerns a villain wanting 3 things that will destroy the world, and Batman trying to put together a team to fight back. The are 'subplots' but a few of these last for literally a scene. Cyborg, for instance, is supposed to have a spin on the Frankenstein's monster thing, where he has to accept what he now is, but the movie literally bins this idea at birth. So you get this bizarre situation where he's supposed to be a sullen guy who wants to be left alone, to in the space of 1 conversation with Wonder Woman is joining up with the rest of the team.
The dialogue is awful. There's so many horrible exposition scenes, so many scenes with people saying things in a manner nobody in the entire history of humanity has ever said. Introducing us to Cyborg's dad, a cleaner suddenly drops a ton of dialogue lead with 'Good night Silas. By the way, I didn't have chance to say, sorry about your son'. The opening has a criminal just caught by Batman basically fill the role of the opening crawl of a Star Wars movie, but written by someone with a lobotomy. Aquaman has a truly hopeless scene with Mera, played by Amber Heard, who brings to the role the ability to fit into a skin tight suit, but not the ability to sell explaining a character's backstory to that character, without it sounding like it was sledgehammered into the plot on pain of death. This scene also reveals that they need to have some imaginative ways to make sure the characters in his solo movie can speak to each other, because boy is the solution here bad. Then there's the obvious Whedon scenes thrown in, all of which you can spot from different timezones, which are riddled with awful banter and particularly poor jokes (there are 3 decent gags in the entire thing). If you think Marvel's stuff isn't funny, you'll think this is as funny as bad trip to the dentist.
The CGI is astonishingly bad for a film that cost as much as this did. Steppenwolf, a bad villain to start with, looks worse than some videogame cutscenes, with dreadful design work to go along with it (and he's barely a character. He's bad. The end). But then you have stuff like a few shots of the Batmobile in action scenes that almost look unfinished, and best of all, Henry Cavill's moustache. You can see his weird plastic looking top lip in loads of scenes where they've thrown some pixel makeup over his 'tache, and it's hilariously bad.
And it's tone deaf. This is a movie that contains a scene where, trying to establish the world has gone to pot, decides to show a couple of guys booting over a crate of oranges in slowmo, followed shortly afterwards by a scene of school children about to be executed by terrorists. I literally laughed at the scene of a coffin being dug up by moonlight, a truly bizarre scene that feels like a parody straight of a bad sketch show.
Even the action is bad. There's hints of better stuff (there's a few very very brief moments of them 'getting' Batman but nothing to touch the warehouse fight from the last film for instance) and one decent sequence, but largely it's really dull by the numbers stuff thats completely outshone by nearly all of its peers. Most obviously they do nothing with the Flash that the X-Men take on Quicksilver hasn't completely blown away. Pretty much the only thing they do in any Flash moment that stands out isn't even done by the Flash. The film doesn't know what to do with the characters. Batman pretty much sticks to vehicles, Aquaman doesn't do much beyond what we've seen in the trailers, Wonder Woman has a couple 'hero' scenes, the first on which is so daft looking you can't take it seriously even if you wanted to. Superman does... Well, what can you say really?
It's... It's bad. There's barely a plot, the villain is awful, it looks ropey as ****, it's all over the place in tone, the script is dreadful... It's a mess. It could have been worse, underneath it's largely competent, it's major flaws, bar CGI, all come from errors in the writing, the cast is mostly fine working with the rubbish they've been given, it lasts 2 hours and literally buggers off at speed. With low expectations you could enjoy it, it requires no effort to engage with it on any level, a few scenes are pretty enough. But wow... BvS is arguably more successful in many ways. Less messy for a start.
It's a damn shame they **** this up. There's stuff to like about the DCCU. Afflecks Batman has potential for a more comic true take, they understand how to make him move and act correctly. We finally have a nod towards a good comic Superman. Wonder Woman isn't a great actress but it just about works. Aquaman might be fun. Occasionally it looks right. But they've **** it. They gave the wrong man too much control, they didn't have the studio controlling where things went, they obviously had no arc planned, they've wasted storylines and misused them, got the tone wrong, built the universe wrongly desperate to catch up, and messed up all the planning. And we get this. And all the other mad ideas they have allegedly on where to go.
What a mess.