Say what you will about SUPERMAN RETURNS...
It certainly had ALOT of great things going for it. The best way to approach any possible sequel/follow-up reboot, is to take what worked, and change what didn't. I can certainly appreciate SR for what it is, and I really enjoyed it when it was first released, but rewatching it again made me realize why so many tend to dislike it. Singer sought to make an introspective, personal story about the Man of Steel, that asked some interesting what-if questions, and he succeeded; But in alot of ways, it really dug itself into a few corners, and didn't leave alot in the way of a new series. I like to look at it as an alternate conclusion to the first two Superman films.
But rewatching those two films (as well as the Donner cut of II, and reading Donner's "Last Son" arc) made me really long for another great Superman film. Poor Supes always seems to get a bad rap compared to his black clad, pointy-eared rival, but I feel that an uplifting, action-packed original Superman story using today's technology would really be something.
Here is what I would keep from SR:
Brandon Routh. Say what you will about the guy, there's no denying he looks the part. Looking a few years older, bulking up even more and more acting experience will make him even more perfect for the part. Let the guy grow in the role, and he could be just as good as Reeve.
Kevin Spacey as Luthor. What's not to love? Sure people complain that he just rehashed the Gene Hackman land swindler bit, but that was the writers' fault not him. Other than that, he was simultaneously charismatic and sinister: a definitive Lex.
The costumes/set design: IMO, Superman Returns just had such a great timelessness, combining modern technology with the fashions of the 30's and 40's, will certainly help it stand up well in the years to come in those respects, kind of like Burton's Batman (and unlike the 1978 film, where the contemporary fashions and Metropolitan sets SCREAM seventies. Fortunately, it still holds up great despite that.)
John Williams themes. Maybe not hit them over the head like before, but at least use an original score that usefully references them. Williams is one of the great masters in the the field if not the greatest. You could compose a new theme like they did with Batman, but it would only draw comparisons, and there's no beating Williams in his prime.
What they need to change:
TONE! TONE! TONE! Give the movie a relatively uplifting tone, with the right amount of action and violence. No more drab cinematography filled with depressing colors.
Villains. Keep Luthor in the background and reinvent him as a full-time business man, but throw in some monster or alien Supes can go toe to toe with.
Lois. RECAST. Nothing wrong with the character, just Bosworth and the way she was written. Just ignore the Richard subplot and the kid, and we should be fine.
I personally don't really care if they redid the origin, as it was already done so perfectly in the 1978 film. We've already seen it in the movies, the cartoons, the serials, and the TV shows, do we really need to drag it out again?
If audiences have to see it, do it like the 2008 INCREDIBLE HULK, and keep it to the opening titles.
A great new Superman movie is simply begging to be made. Forget about a straight sequel and a "Superman Begins" reboot, just make a bad ass Superman film that takes what worked from RETURNS and do something otherwise new.