I think that people see Superman's invulnerability and "... and the kitchen sink" list of superpowers as proof positive that Superman is inherently a weaker and less interesting character than Batman, and while I do tend to think that Batman is probably my favorite comic character and franchise, I also think that this dismissal of Superman is selling Superman short.

The issue, I think, is that people are only looking at surface-level conflicts, and when you are only looking at the surface-level, Superman seems far more shallow and less nuanced. If you boil comics down to "Guy A fights guy B", Superman's powers make him inherently over-matched against any opponent people can identify with. However, it is when these comics explore deeper issues that they shine, and both Batman and Superman have them to explore.

For Superman's, they come both from external and internal conflicts. Internally, there is the question of whether it is right for Superman to interfere with humanity. This was actually addressed, albeit absurdly ham-handedly, in Superman IV - People have nuclear weapons, which threaten all life on Earth... is it right for Superman to tell people they're not allowed to have nuclear weapons in order to protect them? At what point does he cease to be a protector and Samaritan, and start becoming a well-meaning dictator?

What's more, another internal conflict is that, as powerful as Superman is, he still has his limits. He is, after all, just one man, even if he's a man of extraordinary power. And as a man, he can only do so much. How is he to put that power to use? When he so clearly values life, how must it tear at him when he fails to save someone?

Externally, much of what makes Superman a potentially powerful story is his strength as a symbol. All that "truth, justice and the American way" stuff. Some of the more interesting Superman stories aren't even about him, they're about the way he affects the world around him, both for good and bad. To some he's an inspiration of hope and something to aspire to. To others (most notably Lex Luthor), his mere existence is a mockery to the strength, ingenuity, independence, and ambition of humanity. What does the world look like when people see a force of pure good, the epitome of what humankind aspires to be?

It may be hard to see these sorts of conflicts when you're looking at Superman fighting some alien or robot or standing all smug as a bank-robber stupidly tries to shoot him. Often this is the fault of those who write his stories - they see his fantastical elements as his main draw and highlight those, and ignore his humanity. So you get dumb strongman fistfights. But it's that same sort of thinking that brought us the Adam West and Joel Schumaker Batmans, which tried to focus on the fantastical rather than the humanity, and suffered for it.

Superman can be an incredible figure to place at the center of a story, so long as the storyteller remembers that the interesting part isn't what he can do, but what that means for who he is and the world around him.