I liked Watchmen's take on a Superman-like character. Morally gray stuff like Dr. Manhattan being used to win the Vietnam War (as an analogue of nuclear weapons) and him becoming so powerful he becomes detached from mankind. Why would Superman care about us, when we are like ants to him?

There's also Red Son, a truly interesting take on... commie Superman.

But there's so many times you can tell those stories, I guess. Superman is a really boring character.