Because I'm bored, here's rough notes for a setting start.
All kinds of heroes (mutants, transformed, robots, magic, aliens, etc.). If you can justify it, it can exist. Heroes have been public for a generation, starting with Galaxy in 1979. (Yes, that means that there were decades of superhero comics to draw from.) Some think that the pre-existing comics shaped what came.
North American superheroes appeared after the meltdown at Three Mile Island. Surely it wasn't the radiation; dirtier bombs had been exploded in earlier years. But if metahumans have long been with us, the incident at Three Mile Island spurred them to be public. Galaxy had just come into her powers, so she is no proof either way.
In the recent past, there has been a battle between good and bad on an unprecedented scale, though the numbers of metahumans were never so high that everyone was affected. At the end of it, the various groups were shattered. Oh, there might be a member or two left of some (even most) of them, but the : mighty battle between good and bad, has destroyed both and left power vacuums. (If we ever want to bring them back, they aren't dead, they're in the massive crossover event Clandestine Infinities.)
The person on the street in North America would recognize as good-guy teams the Liberty Union, the Justice Vanguard, the Appeal, the Shadow Cabinet, and the Golden Balance, and hero names like Exalted, Galaxy, Nimble, Spicer, Suitable, Maximan, and the Sky Clan. The same person would know about Doctor Apocalypse, about Count Infinity, and about the Darwin Association, who have all very publicly tried to destroy the world.
They are less likely to know about the other criminal organizations, such as the Benevolent Organization, the Parliament of Hunters, the Federated Autarky, and the Underworld Syndicate. Those organizations are in disarray, though they're likely to be re-built in some form or another.
The Atlanteans have only just come out in the last fifteen years (since the disasters off the coast of Africa), though they claim to be older. There seem to be at least three types of Atlanteans, ranging from the human-looking sub-mariners through the merpeople to the Deep Ones. They are beginning to be a threat to shipping, though nominally some counrties have treaties with them. (Adventure idea: protecting a watery caravan.)
Fight club exists, and it's for supers. Imported from Thailand, the underground combat rings for metas are a place where heroes and villains have both trained.
This is a time when super villains start to appear, eager to make names for themselves and consolidate control. At the same time, non-super organized crime--the mundanes--are trying to re-grasp what has slipped from their fists.
There is no obvious government organization dedicated to metas--that function has been distributed among all the different alphabet-soup groups. There is fierce rivalry between the groups.
But you don't start with any of this--you start with something small. A group of female villains who have all adopted code names that start with B (who call themselves the "B Hive") have decided on something flashy as their coming out crime. They expect police involvement and maybe a superhero or two, but the point is to demonstrate that they are tough and can't be stopped.
This first crime is a pretty standard bank robbery, except that they have their escape already planned--they expect that the psionic powers of one of their team will let them leave whenever they want.
There are more members than the ones on the job, but this caper is Brawn, Blister, Blackbird, and Bungee, with Brainz held in nearby reserve.