This was neat, concise and clearly written. For a short piece of text (comparatively, some of the entries here are crazy big) you crammed a great deal in.
I think the mechanics are fine but what I would have liked to see more of is the side-kick theme, so emphasis on assisting the heroes, setting up their corny one-liners and possibly being a hot-headed youngster whose rashness sets up the scene for the superhero to shine. Additionally, it would be nice for the status of superhero to be a goal of the sidekick, maybe as an endgame scenario ("There's nothing more for me to teach you, Gravity Girl!").
Of course, the fact that the side-kick has weaker powers than the hero will help to facilitate this, but it would be nice to have that embedded in the mechanics more solidly.
The play through narratives were great. We need to see more of these in RPGs, they used to be such a common feature. Yours were also nicely written as well as demonstrating the rules of the game in practice.
Great work.