Superman has always bugged me. The idea of dressing up in a special outfit and going to fight crime I can sort of understand, but it makes more sense for Batman than for Superman. Batman devotes nearly his whole life to fighting crime; even those token times spent as Bruce Wayne serve mostly to provide a cover (and income) for his crime-fighting. Batman needs a base, equipment, and intelligence gathering. And after all, it's not like Bruce Wayne can just disappear - if he did, all of the nice gadgets that makes Batman a real threat to the underworld would disappear too.
On the other hand, look at Superman. He's super-strong, super-fast, has laser eyes, X-ray vision, super-breath, flight, and invulnerability. He doesn't need money or a base. In most iterations, he doesn't even need to sleep. There's no reason for him to have a secret identity, from a crime-fighting perspective. The reason for Clark Kent must, therefor, be personal.
One of the biggest things I hate about Superman is kryptonite. To me it always smacks of a cheesy plot device. Authors and screenwriters seem to feel that Superman is too powerful, so kryptonite is needed to add in some element of danger, so that the audience actually feels suspense. They actually do the same thing in some of his rescue scenarios - Superman is almost always just barely strong enough, or just barely in time. But to me, that seems the wrong way to go. It should never be a question of whether Superman will succeed.Superman should be at risk for failure not because his powers don't work, but because the situation doesn't call for the application of brute force. He should have trouble fitting in with human society, wanting desperately to be accepted but not really knowing how to interact with people. The only reason that people adore him as Superman is because he saves their lives; as Clark Kent, he has no power, and without the grand deeds his attempts at charm just look weak and pathetic. Add to that the fact that he's kind of a uncompromising zealot, and you can see how he'd have problems when he can't hide behind having incredible powers.
And think about how tortured he must be. His super-hearing, depending on which version you go by, spans the whole world. With his super-vision, he can see through walls and watch the whole city at once. He knows that every second he spends as Clark Kent is a second that he's not saving someone from death. He can hear suicides screaming as they plummet to their death. He can hear women being raped, children being beaten. And the Clark Kent persona is so valuable to him that he stays in it, and only rushes off when there's a bigger emergency. Let's assume that Metropolis is like New York City. That means per day, there are 1.4 murders, 2 forcible rapes, 59 robberies, and 66 aggravated assaults. Those are just the violent crimes - that doesn't include all the fires, accidents, suicides, burglaries, natural disasters, etc. And yet Superman still spends a third of his time at playing human as Clark Kent. How did he come to that decision? Why does he choose to let people die?
One of the most common arguments against God is that there's still evil in the world. If there's evil, and God has the ability to stop but doesn't, then God must not be good. To my mind, the same applies to Superman. Especially after he has an interview with Lois Lane, wouldn't the public hate him for all that he doesn't do? Can't you just see the angry mother crying through an interview? "Superman stopped the train from derailing and then flew off, fast as lightning. Not three minutes later, my son was shot to death in an alley by a mugger. Superman was the only - theonly - one that could have saved him, could have stopped the bullets, and instead he just flew away. Where did he go? Why was my son less deserving of life than those people on the train?"
Or let's say that Superman actually does try to stop every crime in Metropolis. Even he isn't sufficiently powerful to stop them all, so he'd have to invent some kind of sorting algorithm (such as "If I have to choose between saving a life and saving property, I will choose to save a life"). And how would he decide? He'd be utterly crucified by the public, pretty much no matter what he chose, and it probably still wouldn't help him with the grey areas. People would write letters to the editor asking why Superman doesn't stop abortions from taking place, or they'd complain that his super-hearing and super-vision are tantamount to panopticon surveillance, or they'd complain that he's not doing anything about the prostitution problem, or they'd complain that he's exacerbating the plight of the poor, or they'd complain that he's contributing to the overpopulation of the prisons. A city with Superman working at full-speed, all the time, is one where he becomes the de facto police, and the policies that Superman enforces become far more important than the ones that are made by politicians.
You know what I think Superman feels when he comes across supervillains? I think he feels relief. Because here, finally, is something big and unambiguous, a true evil that can be stopped for good instead of a systemic problem that doesn't have a good solution. When he punches Luthor into the ground, he can forget about the liquor store robbery he stopped a few days before, and the man he put in jail whose children will grow up without a father. When Doomsday comes down, Superman can stop thinking about whether delivering food to starving people in Africa is depressing the demand for local crops and perpetuating the cycle of hunger, and just solve a problem by using his fists.