There is no one size fits all model for superhero movie universes, and every company has tried something incredibly different. As of right now, the gold standard is the Marvel Cinematic Universe, and there are a few keys to its particular brand of success. One of the most important elements in Marvel's broad appeal is the fact that its movies don't take themselves too seriously, and Ant-Man's Evangeline Lily apparently thinks that's something that the DCEU could learn from them.
Evangeline Lily recently made an appearance at Emerald City Comic-Con (via Bleeding Cool), and made her particular distaste for the DCEU's tone fairly apparent. Although she had nothing specifically negative to say about the actual quality of the silver screen DC adventures, the Ant-Man star pointed out the fact that DC's films "take themselves too seriously." She's an authority on this type of tone as well, as Ant-Man remains arguably the funniest single Marvel movie to date.
There are a few schools of thought when it comes to how to approach these comments. For starters, she is correct in this assessment. DC films do take themselves far more seriously than Marvel movies, and there's an argument to be made that such tone doesn't work for every character. In particular, one could easily argue that Man of Steel's muted tone and color palette didn't match the inherent brightness of the character we all known and love from the source material. Serious is one thing, but DC can get pretty grim at times. Whether or not that's a good thing is in the eye of the beholder.
Beyond that, it's worth pointing out that a "serious" superhero movie isn't necessarily anything to scoff at. Look no further than the film that debuted this weekend for an example of that. Logan is arguably the darkest and most serious superhero movie since Christopher Nolan's Dark Knight trilogy, and it's being praised for its grim take on comic book subject matter. Does Wolverine lend himself to a serious story more than characters like Superman and Wonder Woman? It's possible, but I would advise against painting in broad strokes and making claims that an entire universe is "too serious" in any way shape or form.
We will ultimately have to wait and see whether or not DC will stick with this stern and serious tone in the long run. There seems to be a massive shift occurring behind the scenes of the DCEU (particularly with the recent announcement of a Nightwing movie), and that could lead to some substantial tonal changes in the coming years.
The DCEU will continue to expand when Wonder Woman hits theaters on June 2, 2017. Evangeline Lily is currently set to make her next appearance in the Marvel Cinematic Universe when Ant-Man and The Wasp hits theaters the following summer on July 6, 2018