DC is undoubetly a powerful universe (At least compared to Marvel, maybe not Image since they have characters like Spawn and GOD.), and Superman is probably the most powerful hero, yet he has enemies like Lex Luthor, Toyman, and the Prankster. Now, Luthor is undoubetly cool and he can pose a threat to the big S because of how cunning and intelligent he is. But the other two? Really, even considering Luthor's cunning, there just three normal men. Morgsn Edge is a norman guy also isn't he? I don't know much about him. I know that Superman has some powerful and unstoppable villians like Doomsday and Metallo and Darkseid I guess. Brainiac is cool as well, even though I hear that they retconned him. But really, for such a powerful character, he has one of the weakest Rogues gallery in superhero comics.
I have to agree. The reason is, of course, that the theme of Superman's rogues' gallery is "outwitting Superman"... and that doesn't take a load of physical capabilities to accomplish. Guys like the Prankster, Toyman, J. Wilbur Wolfingham, and that ilk mostly want to just get their schemes to fruition without having Superman stop them, not particularly endanger Superman himself. Which can be an issue if you expect the villain to be a real threat to the hero, which isn't often the way we should read Superman books. (Superman is the ULTIMATE survivor. No matter what the villain does, we know he's making it. The question is, "Will anyone else?")