Over the last three years, we've been treated - depending on who you ask - to three installments in the DCEU. While these movies have received mixed reactions (take a look at this early review of Suicide Squad for more on that), one of the largest factors of this has been the tone. Particularly, Man of Steel and Batman V Superman: Dawn of Justice have both been commonly referred to as "dark" and "hopeless," and these criticisms have gone far enough that fans have even tried to prevent Zack Snyder from directing Justice League!
With the direction that Zack Snyder has taken the DCEU, some fans are losing hope. However, the Wonder Woman and Justice League trailers seem much lighter and more hopeful (here are the trailers if you haven't seen them yet):
With these trailers, it's clear that the DCEU is heading in a more hopeful direction. In fact, Geoff Johns views the DC Universe as "optimistic" and "hopeful," and with him as the head of DC Films, the trailers above are pretty accurate in telling that the DCEU will be lighter and brighter than it first began.
Myself as a fan, I'm looking forward to the DCEU, and believe that hope, optimism, and light will begin taking center-stage. As for the other fans that would disagree, I would like to reassure them with an analogy that could restore their faith in the DCEU:
A Departure from our World via a Day-Night-Day Cycle
Although this sounds a little complicated, it is actually pretty simple: the DCEU starts off as a usual day in our world (Man of Steel), then the day turns into a dark, grim night (Batman V Superman), and finally, the night turns into a day brighter than any other that makes the world as though it is a completely different place (Justice League). This analogy attempts to show that as the DCEU progresses, the world is shifted from the dark and cynical world that we live in to the brighter and more hopeful world that the DCEU will be. It's a reassurance that the DCEU will become better as time goes on. This can be seen by looking at each phase of the cycle in more detail:
The Beginning Day: Man of Steel
Thanks to the genius mind of Christopher Nolan, Zack Snyder's adaptation of Superman has been kept in our world in a way that allows the DCEU to remain as realistic as possible. Clark Kent is faced with moral questions even when he's raised to do what's right, threats have realistic casualties, and the philosophical view of aliens, hope, and humanity are portrayed from a very real perspective. And toward the end of the movie, according to the analogy, the sun began to set on the day as Superman was faced with a destructive battle against General Zod and a decision that would push his character to the limits.
The Darkest of the Night: Batman V Superman
Taking place during the final events of Man of Steel and onward, BvS finishes the transition from the day in our world to the worst of the night. This was accomplished by depicting the cynicism, fear, and hatred that the world would actually feel toward a god-like being; who defeated General Zod while innocent people died in the process. As the world's view of Superman grew negative - and Bruce Wane's hatred and fear of what Superman could become increased - the last light left of our world disappears during the night, bringing the DCEU into the darkest point that it will ever face in this cycle. However, toward the end of the film, the first light of the dawn begins to show as the Trinity bands together to defeat Doomsday; and the world becomes inspired by Superman's sacrifice to save humanity.
The Glimmering Light in the Night Increases: Suicide Squad and Wonder Woman
After the Death of Superman (the capitalization is intended), the night has past its darkest hour, and the first light of dawn in the sky begins to increase. This is apparent in Suicide Squad by the increased humor and slightly lighter tone (which is ironic for the dark movie that it is). From what we can tell, the light increases even more with Wonder Woman: the level of humor is equal or greater than Suicide Squad, the color saturation is higher than the previous two Justice League-based films (making colors more vibrant), and there is a more comforting sense of hope than the previous two films - in a way that may possibly be greater than the hope in Man of Steel!
The Sunrise of the New Day: Justice League
After the increase in light and hope - from Suicide Squad and Wonder Woman - that has and will have come to pass, the cycle is complete with Justice League. After all, the unity of the seven... I mean six, founding members of the Justice League, the tone being more upbeat and hopeful than any of the previous films (seriously, have you seen Barry Allen in the trailer?), and the resurrection of Superman! The movie itself screams hope and lightheartedness!
"The night is darkest just before the dawn. And I promise you, the dawn is coming." - Harvey Dent, The Dark Knight
Although this quote is from a completely different franchise for DC Comics, it still has prevalence in this case. Batman V Superman is easily the darkest film in the DCEU to date, and there are clear signs that the DCEU will be brighter and more hopeful on the day that the Justice League stands together. The day that Superman returns. The day that hope takes center-stage in the DCEU. After all, it's like it was foretold in the very beginning:
"You will give the people of Earth an ideal to strive towards. They will race behind you, they will stumble, they will fall. But in time, they will join you in the sun, Kal. In time, you will help them accomplish wonders!" - Jor-El, Man of Steel