One of the things that stood out to me and got me interested was the huge variety of very different characters and backstories.  Maybe something having to do with that, different people in different places?   

You could also do something like with Superman, given how powerful most of the cast is—the struggle to reconcile idealism with reality, fighting and surviving through scenarios where raw strength and fighting aren't the solution, having incredible strength but being forced into situations where that strength isn't the factor it could be.  

Something about cooperation?  Something about friendship?  Something about giving people who might seem like total potatoes, either due to power level or personality, a chance to prove themselves?

Also really like Drag's thing, about purpose.