I saw the Dallas Theatre Center production. My father is a huge Superman fan (and saw the original Broadway production as a kid), and we flew there specifically to see it. I grew up with the cast recording, which I always thought had a few good songs, but was overall too cheesy. I also saw the TV movie version a long time ago. So basically, I came into the production being familiar with the show and already having some opinions about it. I thought the Dallas production was fun, but that there was no way it would ever go any further. Even with the new book, Superman is just a ridiculous idea for a musical (and I really like Superman).
They also cut the song "Revenge" (and the character who sings it), which was a shame. If the show had more fully committed to its own silliness like it did with that song, it might have been something. Otherwise, it's really just a very niche show for cross-over Superman/musical theatre nerds.