Warner Bros. has had a rough go at it with the DC Extended Universe. After seeing Disney and Marvel Studios flourish with the Marvel Cinematic Universe, it's easy to think that Warner Bros. would have been able to simply replicate what seems to be a winning formula
That... did not happen. Instead, the studio opted to take a darker, grittier route, and it's suffered for it. Now notorious for taking its iconic characters in bleak, distressing directions, Warner Bros. is in the early stages of attempting to brighten its universe, and thus its chances for future success.
Following a fairly unsuccessful attempt to lighten the tone of Justice League, the DCEU's new direction has been teased in the synopsis for Shazam!. If done correctly, the film shouldn't feel like anything that has come before it; it should be superheroic in nature, of course, but that doesn't mean it has to be "realistic." In fact, it should lean towards being more unrealistic, to really emphasize the experiences young Billy Batson is about to go through.
Fans have already been promised a more fun, lighter take on the live-action versions of DC Comics' most popular characters, but the reality has been less than successful. Ahead of the film's release, Ben Affleck went on record to say Justice League had a "very different from the tenor of the last movie and there’s also more room for humor.” Sure, there were more comical moments in the movie than its predecessors, but a lot of the humor either didn't land well or cheapened the moment at hand.
Worse, while The Flash was the comedy relief in JL, Ezra Miller's solo outing now appears to be an ensemble piece based on the bleak, alternate-timeline storyline of DC Comics' Flashpoint event. In the comics version, Bruce Wayne is dead, Superman is being held by the government, and the world is being destroyed via a war between Wonder Woman and Aquaman and their home nations. Basically, the storyline can't be too fun since it needs to be taken seriously, and despite numerous development issues, Warner Bros. is rumored to be intent on bringing it to life.
Wonder Woman had some fun moments, sure, but it was a serious movie at its heart, and its safe to assume the sequel will follow suit. The Suicide Squad sequel is almost in the same boat, it had some fun moments but it was still quite moody and dark. Aquaman, despite having a charming, dude-ish lead in Jason Momoa, is being directed by famed horror director James Wan, so it's unlikely that it'll be an joke-filled laugh fest. It all comes down to Shazam! to inject some much-needed enjoyment into the DC Extended Universe.