The tone of the DCEU was all wrong. In Man of Steel its tone was way too dark, way too bleak and too ambitious for its own good. Batman Vs Superman was just more of the same and even worse somehow. Wonder Woman worked, because it got the character right and the story was good. Justice League was... at least a movie but it ultimately did not work, mostly because it had a lot of the same problems Batman Vs Superman had. I think JL's biggest weakness is the heroes just lack the same kind of depth and emotional attachment we as an audience grew for Captain America, Iron Man, Black Widow, Ant-man, Star Lord, Gamora, Groot, Drax, Black Panther, Hawkeye, and so on.
I think a big part of the problem is Zack Snyder. The guy is just... he's only like a notch or two above somebody like Michael Bay. Like Michael Bay, he doesn't understand why fans love the characters in the DC universe. When he's not blowing shit up or doing product placement, he sometimes gets way too artsy fartsy, and as a result what he thinks is wonderful cinematography is a lot of pretentious bullshit.
Now obviously, the likes of Shazam and Joker were much better, but those AFAIK have nothing to do with the DCEU. Birds of prey was really good btw.
I've generally speaking been put off DC movies for a long time mostly because of all the assholes online shit-talking Brie Larson and Captain Marvel.