I'd be open to a period piece or a contemporary setting, but I think bringing Superman's power levels way down and reducing the level of fantasy would be the wrong way to go.
I just watched Superman: The Animated Series
on DVD and watched and listened to the special features, and the view Bruce Timm and Co had of how to make a Superman series is the approach I'd like to see in the feature films (and the approach I think the general public would respond to the most favorably), namely that Superman is a powerful science fiction superhero who needs to operate in a science fiction milieu and face powerful science fiction villains. They toned his powers down somewhat from the comics, but he was still powerful enough to be capable of dazzling feats, and they gave him powerful villains who could really challenge him. That's the way to go.
Also, in terms of characterization I think the mistake SR
made is that Superman was too much of a quiet, withdrawn loner. That's just not a Superman that the public, or at least much of the public, is comfortable with. A certain amount of angst about finding his way in life and reconciling the different parts of his nature has often been an element in Superman stories (from the Chris Reeve films to Smallville
), but at heart he's always an optimistic All-American hero with a commanding presence. If there's a reboot it should be true to that.
As for the storytelling structure, I think there would be a lot to be said for a reboot that just dives into things in media res
and doesn't have flashbacks at all - just have the elements of the universe in place and let the audience discover them as you go, with the origin story left unsaid.