After staring at the Marvel Comics version of the Nine Worlds I posted here, I realized that I didn't want to come up with my own "fantasy superhero" world, I pretty much wanted to play around with a Norse one. (Besides, coming up with your own world is a lot of work! Why not just adapt one that is already there?)
So, the focus of this campaign is demigods. I interpret this as something likethe offspring of gods and mortals, or the lesser offspring of goods like Thor, Odin, Freyja, etc. Other possibilities are available, too, if the characters wish to explore them. Since Walt Simonson's run of Marvel's Thor comic inspires me so much, it'll probably be a major influence, but I won't be using its continuity. One idea that I do like is that Midgard is really our world, so the PCs can be modern characters who discover their divine heritage and the Nine Worlds from a modern pesrpective. The ones who do know something about Norse mythology will have some advantage, but I feel like I can change any details to suit me; the ones that don' know much won't have to grasp everything at once. Perhaps the world the characters know is the illusory one? This is starting to take on elements of Percy Jackson, too. I think I'll resist the urge to include a version of "Camp Halfblood" though I'm thinking of including elements of "American Gods".
Time to dig out the reading material, I guess. More as it develops.