Just a thought...while we know this film will start in the middle of the action, and this Superman will have already been Superman and known to the world for 2 or 3 years it seems--but there is something that makes me slightly worried. Not that I want another origin story--to which I also think not doing another origin is the right call--It worked for Matt Reeves' The Batman which is not an origin story, but it had at least some backstory and took time to develop most of the characters. It felt like a beginning in a way without actually taking place in the beginning.
In line with my last statement though, I've always felt something noticeably off when I've watched other Superman animated media, specifically with Superman: Doomsday, All Star Superman and Justice League: War (a movie which I loathed by the way). It's hard to describe what the issue was for me. I think in part, it had to do with the new voice actors which seemed to be a factor. But it didn't feel that way entirely when I watched Superman/Batman: Public Enemies and Apocalypse. You had Tim Daly, Kevin Conroy as well as Clancy Brown, and if you were already familiar with them, then you didn't really need a backstory. I didn't have an inability to care about the characters. But in Justice League: War, Superman is introduced as more muscle than man, violently aggressive and lacking any kind of emotion or depth.
I'm not too worried about Gunn interpreting Superman that way, and I feel fairly confident Gunn will give Superman enough humanity. But in most of these animated films, when Superman was introduced in the middle of the action, as well as other characters such as Lois, Perry and Jimmy, something felt off. I don't know how to explain it. I did enjoy All Star Superman, as well as Superman vs The Elite, but something felt missing to an extent. In some ways, when they show all these characters, it's as if the expect us to already be familiar with the characters.
I think it's when an average audience watches one of those films without any real introduction or prior knowledge to Superman's background or origin, they might find it hard to relate to Superman who's this all-powerful being from another planet who's all-good, but they may not be aware of when and how long he had been raised on Earth, because for me, an important factor of the Superman character is that he is human. Yes, he's from another planet, but he was raised as a human. Superman vs The Elite does interpret Superman as all-good. For a new audience member, I don't know if they would be able to relate. What helped me enjoy it more was the fact that George Newbern did the voice, whom I was already familiar with as Superman in the Justice League animated series.
In All Star Superman, while obviously not an origin story, it focuses on Superman's condition. He was dying of cancer. They show us that Superman and Lois have already had an established relationship. I wonder how a new audience member jumping right into this story would have been able to relate or sympathize with these characters, particularly Superman who was dying. I still enjoyed the film though. I feel like if Gunn started Superman's first film in the DCU with a direct adaptation of All Star's plot, it wouldn't be a good way to begin Superman's story. Pretty sure Gunn won't do the cancer story though. I think it might work for a third sequel.
Just saying, for non-fans, they have notoriously complained that Superman is not 'relatable' and I couldn't disagree more. It's ignorant.
I think what helped audiences relate to Superman more in the CW series Superman and Lois was when they gave a brief introduction of Superman's origin to the present day in the pilot. This series aside, I felt Reeve's Superman was relatable enough in the Donner films...even Superman IV. The Smallville series too. Superman the animated series, most of the time, Superman felt relatable, but I found him even more relatable in Justice League and Justice League Unlimited.