As I was chatting with a friend about the pros and cons of 4th edition D&D and how I could not possibly run a fantasy campaign with it (I will get into that later), an interesting thought struck me. Out of the box, 4th is remarkably close to a superhero game! All of the trappings are there. You have tons of powers, all of which are very mechanically similar, but with lots of status effects to differentiate them -- thereby simulating guns, lasers, claws and mutant powers with the same set of rules. With healing surges, you have very resilient characters (though you would have to find some way to activate them without a healer archetype). You have minions!
Heck, if you just renamed the classes and powers, you might be able to pass 4th Ed as written as a superhero game.
I wouldn't do that though. I think some modifications are in order to truly complete the transformation. I would likely ditch the concept of a single class/character and go for some kind of dual-spec system for a more mix and match approach to characters. So you would not be a "Fighter". You would be a Superstrong/Fire Blaster. I think this would allow more flexability and synergy in character builds. I think a slick way to handle super stats would be in order as well... not sure on that one though.
Otherwise, most of the rules would work as written. Sounds like a side project!!!