The Mary Sue’s advice for the future of the X-Men franchise makes interesting reading for a superhero GM, an adapter of source material, or anyone looking at any setting’s Weird Level.
“Use your badasses sparingly” is largely up to the players, but can also apply to NPCs. Obviously, a big superhero story with no action would be strange (but doable) but there’s definitely such a thing as too much.
“Stop making everyone into teenagers” relates to adaptation in particular, but also to the setup of Xavier’s as a Wizard School for mutants and how that relates to a wider world.
“Not everyone wants to be an X-Man” concerns NPCs, mostly, assuming the PCs have chosen a side in the main conflict, if your setting has a defined conflict. If not, they may well want to make their own way. In either case, having more options for allegiances, shifting alliances, betrayals and places to run to when things go wrong can add a lot to a setting.
“Crack-A-Lackin': How Realistic is Your Universe?” - set a Weird Level and pretty much stay there. Something this series has failed to do.
“Stupid Human Tricks” is about the stakes in the setting’s conflicts. What’s the point of fighting for humanity when humanity doesn’t just hate and fear you but is also nothing but trouble? What have the Rebel Alliance done for me lately? Why bother saving Arkham when all the police do is arrest us? Personalising a larger conflict (or a big organisation like the PCs’ patrons or enemies) can make everything count more, and making the NPCs involved interesting - and the allied ones actually helpful - can help too.
“Build inward, not outward a.k.a. Less really is more” is about NPC bloat, something I’ve been guilty of in the past. Who is vital, who can fill multiple roles, who is there because they’re there?
“Use the metaphors in the material” is targeted at the X-Men movies in particular, but can also apply to any adaptation. What do people love about a setting, what is key to it, what is interesting but nonessential and what can go?