What I think WW had going for it was an insanely good word of mouth that made people go "WTF, DC actually dropped a good movie?!" after a string of shit, coupled with the whole girl power narrative that promotional material would latch on to. WW can do X, Y, Z and on top of that, she's a WOMAN! Also had a narrative of there never being a WW movie in the big screen and they have a WOMAN director etc, probably got asses into seats.
Would WW's inclusion in JL alone cause a lot of people to watch the flick? Looks like it didn't. Coupled with the fact that Zack Snyder gets a lot of shit and most don't like Supes or Batman's portrayal leaves The Flash, Aquaman, and Cyborg as major selling points.
Superhero shows are trash
Also Flash, Aquaman and Cyborg cannot be as strong selling point as say the "B characters" from Marvel in the Avengers were. If the big boys were Cap, Iron Man and Thor, they had the Hulk in waiting and nothing wrong with the three named DC characters but they are not as entertaining as him for a big movie.
Well, WB has made many mistakes with their shared cinematic universe. First, after MAN OF STEEL sputtered after its amazing opening weekend, they should have moved away from Zack Snyder and tapped someone else to spearhead the movies. Then they made the mistake in assuming that MAN OF STEEL's disappointment was Superman himself, so they threw Batman into his next movie and slowly transitioned it from a sequel to a Batman-centric film. Apparently, no one learned any mistakes from MoS because they not only repeated those same mistakes with BATMAN V. SUPERMAN, but compounded them too. Then we got SUICIDE SQUAD, which never should have happened (at least at that time). WONDER WOMAN was a nice surprise, likely because it was the one movie since MoS that they allowed the director to make the movie, except Patty Jenkins appears to be a better director than Zack Snyder. With JUSTICE LEAGUE, this movie was doomed from the start I think. From sticking with Zack Snyder to the release date to the plot, I just think it needed to be a home run with critics for it to have any chance.
I haven't seen Suicide Squad since it came out in theaters. Suicide Squad to me was someone trying to convince WB they could make a GUARDIANS OF THE GALAXY film with more interesting characters. It was just a misfire from start to finish, and was a film that needed to come out much later than it did.
Trying too much too fast. Cramming the exposition of multiple characters and an entire universe in three films. Add to that a director for three of them (with their most important characters) who has a very polarizing style of directing. Where I think they can rebound is focusing on solo films with their characters. Flash, Aquaman, Wonder Woman, Shazam. Let the universe evolve then do a second team-up film where we don't have to see how they come together, they can just appear and take on a more serious threat.
What I think DC has going against them is that if they went that route (solo films followed by a team up) they would be seen and probably called out for ripping off Marvel. They went a different route (Having a team up movie and then solos) and everyone wonders, "How come they don't do it like Marvel?!" Lose-lose.
Superhero shows are trash
What went wrong? I think it's harder to point out what went right LOL.
I was astonished to see how little they managed to get the characters right. Aquaman was Conan, Barry was an annoying comic relief that wasn't even funny and Wonder Woman could have been better explored. Batman was ok and Cyborg was closer to his comic self, but since his current characterization is pretty dull and depressing, this is one character I wish they changed.
Superman was on a whole other level of shitty writing. "Can you bleed" made me cringe hard.
All in all, it was a pretty terrible movie, with bad CG and an even worse plot. Only the world's best marketing could have saved it from failure.