The concept of the last Supers game I GMed was loosely based upon some of the story ideas from The Watchmen and from Mystery Men.
Silver Shadow (the main hero* of place called Paragon City*) had recently been found dead inside of the place he lived. Strangely, there were no signs of forced entry, and none of the security cameras showed someone entering the building. However, there were some obvious signs that he did not die of natural causes. The PCs were all lower-tier heroes who had some connection to Silver Shadow or some reason to care about his death. The players created their own heroes. I did allow what were essentially clones of some Marvel and DC characters, but I worked with each player to fit their concepts into a different world with different assumptions, and this lead to unique characters.
*I know there is a MMO based in Paragon City, but the game had no relation to that. I just liked the name.
*What I mean by "main hero" is that Silver Shadow was analogous to Batman in Gotham City or Superman in Metropolis.