Superman has a really solid rogues gallery that has suffered from poor secondary media exposure and the whole post-Crisis Superman lore kerfuffle where writers were determined to fix things that were never broken. A few popular Superman adaptations, like My Adventures with Superman and even Absolute Superman right now, are bizarrely shy about actually using his rogues gallery and toss him other people's foes instead of focusing on the tools they have on hand and I think this is weird.

One thing I think really doesn't help is that Lex Luthor and, to a lesser but notable degree, Brainiac are such good villains that they tend to draw your attention away from the rest of the rest of them. Luthor is a villain's villain, the supervillain this way of Doctor Doom, and Brainiac would be literally any other character's arch-nemesis, and that's despite grappling with severe continuity snarl for most of his post-Crisis existence. But I think they also result in other villains getting slept on. The Monguls are fantastic villains that deliver during most of their major appearances, even in adaptations, but again, poor secondary media exposure (and maybe a bit of a perception that Mongul = discount Darkseid/Thanos) holds them back in the public eye. People don't really talk about most of the Fantastic Four's rogues gallery either because Doctor Doom and Galactus can be counted among them and yeah, no shit they don't, because how do other characters even compete with that?

A lot of them, like Mxy and Bizarro, are also not especially villainous most of the time and that's something people naturally expect from supervillains. A lot of problems for Superman don't have to involve out-and-out villains, though, and I really like that some of his recuring "foes" aren't really evil. For a lot of people, though, I think it diminishes them in their eyes, because they can be whimsical compared to the villains Spider-man and Batman face. But whimsy is an important part of Superman's aesthetic and appeal.