Justice League was supposed to be the one. Warner Bros were supposed to have learned the lessons of Batman v Superman and Suicide Squad and taken heed of the success of Wonder Woman to make the film they should have been making all along, with an improved tone, a better grasp on characters and less glumness.
They had a lot on their plates, to be fair, with a lot of work needed to right the ship, and it does seem from the early reviews that they've significantly improved on what they made prior to Wonder Woman. That wouldn't have been all that hard, but it's still very admirable to note.
Unfortunately, the successes come with a caveat, as there are lots of reviewers who've been lucky enough to see it early (there are still screenings yet to happen) who have come out of Justice League disappointed again. Sure it's better, but it's not great, and there's still work to be done. What remains to be seen now, is whether it will be the success Warner Bros need to keep the DCEU alive and kicking.
In the absence of RottenTomatoes' aggregating the reviews just yet, there's a gap in the market to pick through what all of those critics are saying about the super-ensemble. And fair warning, if you're a DCEU fan already, there's some stuff here that might annoy you.
Hold on to your butts...