I definitely miss Cadmus, the DNAliens, Guardian, and does anyone else remember that crazy scientist Donovan who lived in the bowls of Cadmus and caused all sorts of trouble? Loved that guy.
I miss Metropolis feeling like a character. It used to have so much personality back in the 90's, and it really made the world feel real. Characters like Bibbo, Henderson, Turpin, Ron Troupe, etc., really added to the mythos. I mean, back in the day the guy Clark bought street pretzels from had a name. I knew nothing else about him, but he had a name and I saw him now and then. It added a lot of depth and consistency to the setting.
I miss psycho, child-killing Toyman. Yeah, I know, Im the only one. But Clark doesn't have a proper "Arkham" style foe (the likes of Parasite are too powerful for this niche, Im talking power of crazy here, not power of horror monsters) and Toyman was solid.
I miss Conner of course. And I miss Steel having a larger role in the Super-verse (not to mention the wider DCU, dude could stand on his own if treated right).
I have't seen much of the social crusader lately, since Clark hasn't been a reporter for some time (and it hasn't had much attention in years) and I'd like to get back (in part) to Superman fighting for the little guy. Let Clark tackle the social issues and let Superman tackle the monsters. That's how it should work, and once upon a time I feel like it did, and we should get back to that.
Maxima and Almerac. That's something I dearly want to see expanded on. This is Superman's little corner of the galaxy in a way, and it's criminally underused and undeveloped. I'd
Game of Thrones the hell out of that solar Empire.
And the super-scientist. Superman should be the smartest guy in (almost) any room he walks into. And he should have many science-based hobbies.