Watching the Justice League DCEU live-action film trailer, I finally understood what I have disliked about both DCEU and the New 52 influence over the DCAU.
During the latter half of the Silver Age and the Bronze Age, during the time when writers such as Perez, Wolfman, Moore, and Gaiman were major inspirations for DC comics, the adult superheroes seemed to be genuine adults; in their better issues, Clark Kent and Princess Diana and Hal Jordan and Barry Allen all seemed to be the sort of thoughtful, emotionally and spiritually mature men and women that most readers hoped to be when they reached adulthood (keeping in mind the restrictions inherent to American style comic books).
This continued on in the DCAU, in such series as Batman: The Animated Series and Justice League/JLU.
In contrast, the superheroes of the DCEU and the New 52 seem to be grown-ups the way the more immature and angsty kids might imagine an adult; they often seem to be written by people who have never met an actual adult before (or by people who are exploitatively pandering to an audience that has no idea what actual adults are like) and who don't think very highly of young people.
Thus, the MoS version of Superman mistakes self-pitying joylessness for adult seriousness; the SvB version of Batman mistakes infantile obsession and violence for adult determination. Judging from the trailers, it looks as though the DCEU JL version of Wonder Woman mistakes an adolescently grim cynicism for adult pragmatism; worse, it looks as though the DCEU JL version of The Flash is an awestruck adolescent written by people who have never spoken to an actual flesh-and-blood young person in their lives and have forgotten what it is like to be young.
This is what I regret most about the post-New52 DCAU and the live-action DCEU: every film in it seems to be just another desperate effort to imitiate Marvel's financial successes by replacing the sometimes-realistic adults of the DC Universe with flatly immature parodies of grown-ups.