I just like that they're just cool, and creative ideas. They manage to be incredibly complex characters (Even Superman, as I hate to admit.) but their stories, actions, and attitudes are just manageable and understandable enough to be moldable by any creative mind. I'm into the thinking/fanfiction/video game part that comes afterward, things where you can grasp and enjoy the characters and their interactions and powers more thouroughly, where you can create your own stories based on the epics that have already been told. Sometimes stories go the wrong way, (Like Nintendo's character franchises have been doing...) sometimes they go the right way, (Like Alan Moore's superheroes have done.) and they can explore important subjects in ways that no other story medium really can. Superheroes are a common plot device, to be sure, but when done right, they're anything but cheesy, and can be the most interesting thing some people have ever encountered.