Mechanically, a superhero MMO has to deliver a recognizable superhero experience, and that means being able to cope with what super-characters will want to do: flying, for example, a sine qua non
of the genre. That not only means combat in three dimensions, it means having to build a world in which there's as much interesting scenery above ground level as there is down on the earth. Even the attempt to model superhero combat brings differences from regular MMO play. There aren't that many MMOs in which characters can PvP in the air.
Fantasy and SF heroes also tend to be much more limited in who they can be. You're a mage, you're a tank, you're a rogue, you're a priest. You have a role in the game world's society and in the context of an adventuring team. But superheroes don't need to fit in; they stand out by their very nature, outlandishly costumed aberrations that paradoxically serve to keep society stable.
That's part of why we maladjusted souls love them. Superheroes are freaks. They can be outsiders from an alien planet, mutants gifted with weird abilities, ordinary people transformed in lab accidents. But they're still freaks. They're not normal
. And when you have a genre in which the characters are all supposed to be intrinsically bizarre, and yet embraced by the world (or taken seriously by it in the case of villains) there's little limit to the kind of characters you can think up.
Just about any concept you can think of can be the basis for a superhero character. Take your concept, put the word 'man' after it (or 'woman' or 'lad' or 'girl' or similar pronoun of your choice) and chances are you've come up with a viable character. You'll probably even have ideas for a costume. This is why City of Heroes
has so many character slots per server on each account, and why they've recently started selling optional additional slots. The players are eagerly buying them up.
So, in our view, that's why all the capes. Because players want to explore worlds that are pleasantly similar to our own, just with superpowers; because it's now been proven that you can
make a superhero MMO that works; and because superhero games allow for more freedom, variety and creativity in character concepts than just about any other genre out there.