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Superman is NOT a "BIG BLUE BOY SCOUT". That is Post-Crisis Miller/Byrne BS. Superman, while very noble and heroic, is actually pretty sophisticated. Leaving his parents alive turned Superman into a mama's boy and the dehumanization and demphasiation of his Kryptonian heritage took Superman further away from having vital common ground with Batman because Pre-Crisis, they were both orphans and Superman was orphaned twice. Before Crisis, all of Superman's peers, ESPECIALLY Batman, treated him with complete respect. In the past 20 years, many of them, ESPECIALLY Batman, have disrespected him to varying degrees and Superman has of course flaccidly accepted this. Basically this was when Superman went from being "Kal" to being "Clark".
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The best place to take Superman now is to take inspiration from the earliest version of the character. I want to see a Superman who has much less regard for the system and more regard for right and wrong. I want the strong social conscience back. I want a Superman who would lock wealthy mine owners in their unsafe mine to make a point about unsafe working conditions, the Superman who didn't mind terrifying criminals or even the mayor of Metropolis to make a point. I want to see Superman as the hero of the oppressed, smashing tenements to bits and forcing their owners to rebuild safe housing. And I want him to do it all with a cocky smirk, sneering at the rich and defending the less fortunate.
And even though I'm usually more in favor of a more traditional scientist Luthor, the Lexcorp CEO Luthor actually fits in this scenario quite well. But I would want it to be made clear that Lex IS a brilliant scientist and that's where most of his power/wealth has come from.
As for Clark, he needs to be treated as a disguise and as a separate personality from Superman, but I would say with less silliness than the Reeve version. Something between there and George Reeves. I also think he should occasionally slip and act bad-ass before catching himself, especially if the new movie is set early in his career.
Lois needs to be driven and ambitious but they should keep away from some of they Lois Lane cliches. And she doesn't need to call Clark "Smallville" EVER. Clark is NOT a dumb farmboy. I despise that whole angle. Her romance with Superman should grow as much out her agreement for what he is fighting for as his personal charm and confidence and of course his amazing powers. The audience needs to understand 100%: if Superman lost his powers somehow, it would only slow him down, but it wouldn't stop him. What Kal took from the Kents wasn't silly farmboy naivete; instead it was a STRONG moral sense of right and wrong and a real determination to change things in any way possible, and outside of the legal system if need be.
That's the Superman Siegel and Shuster created and DC took from them after the K-Metal story. That's the Superman I want brought back both in the comics and in the movies. And I feel that's the interpretation that would appeal to today's audiences.
And there's no reason to change the costume. It's based on traditional Kryptonian clothes (art-deco Krypton like Siegel intended), and it's worked fine since 1938.