Superman Returns was worse than being a bad film ... it was simply
bland. The sequel idea is, if nothing else, bizarre (Kryptonite moon, clones, fast-aging Superboy, killing one's own child). I still think it's most valuable element is the conflict of ideologies between Superman leaving humanity on its own and Brainiac's desire to intervene -- especially if Brainiac had been portrayed as less of a mustache-twirling villain as suggested in the outline. If that had happened, the film would have had some significant resonance with audiences.