Brian Azzarello and Jim Lee are slated to take over as the creative team on "Superman" next year. Wow. Great writer. Great artist. I'm still not going to read it because it's Superman.
Superman does not appeal to me as a hero. He's boring. The guy can do anything. How is it a challenge for him to overcome obstacles? Superman is like a character in Chinese mythology insurmountable problem arises... hero quickly and easily defeats problem. Every time. Or at least it seems that's what he should be able to do considering the arsenal of powers at his disposal. It doesn't make for interesting reading.
I'm sure this isn't exactly what happens in the Superman comics, but he's still not a cool hero. Much of the appeal of comic superheros (especially when readers are younger) is the fantasy of our potential to become like the character. When you look at a character like Batman, he's really just a man. He's a guy with a ton of money who has trained himself in detective work and fighting skills to the point where he can operate as a superhero. But he's still just a man. We could do the same thing as him. Most of Marvel's characters' powers are a result of some atomic force (cosmic radiation, gamma bombs, radioactive spiders) or mutation, so there too, there's the dream that we could some day have something similar happen to us. We aren't going to wake up some day to suddenly find ourselves like Superman. Granted, we're not going to wake up and find ourselves with powers like Spider-Man, either, but it seems more plausible.
Other comic heroes (those in the Marvel universe especially) also carry a theme that their powers, while fantastic, can also be a curse. The Hulk has incredible strenth, but can't control his rage; The Thing also has great strength, but he's a big, ulgy mass of orange rock; Rogue can absorb another person's psyche, but she can't touch anyone's skin without potentially killing them; Cyclops can blast through almost anything with beams from his eyes, but he can't ever look at anyone directly without a pair of big, ugly red glasses. These characters are flawed, and as such, we can identify with them more easily. Superman is so far removed from humanity that there's no comparison between him and us.
Besides, his costume is ridiculous.