I'm responding to the first page of the thread. Apologies if I'm out of date already!
There have been some answers to the question
what is story now?. Here's mine. It relates to Arilyn's post too.
Story now contrasts with
story before ie when the table (or the GM) has already decided what the story is. (Eg a typical modern module is story before.)
It also contrasts with
story after ie when there is no story during play, just "stuff happening", and a story is imposed after the event. (Playing B2 KotB will typically look like this.)
The reason that it produces the vulnerability that Arilyn mentions - in my view, at least - comes from a combination of the above. Unlike story after, we care about our PCs and the game is set up to put them at the centre of events as protagonists with dramatic needs. Unlike story before, there is no safety net of the pre-established plot. Caring about your character, and pushing his/her dramatic/thematic interests hard, with no guarantee as to what might happen, can be scary!
What helps make this sort of play work are elements in PC build, action resolution, GM method, etc that
allow the players to flag their PCs' dramatic needs/thematic concerns and to make those front-and-centre, and also
that allow the GM to put pressure on those things.
The only supers RPGing I've ever done was with MHRP - which is a version of Cortex+.
Here's a play report.
I didn't worry about
what the villains' plot was. I just presented the villains and played them in accordance with the logic the system gives them plus my own knowledge of Marvel stuff, and found out what happened next.
In the next session we had the male PCs (in civvies) meet up with the B.A.D girls (also in civvies) at a bar in Washington DC, which started as a social scene and then turned into standard fisticuffs as it turned out that the villains were trying to steal a Stark-tech M-PORV (from memory that's Multi-Person Orbital Re-entry Vehicle - I made it up on the spot) and hoped to get help from James Rhodes (ie War Machine).
An interesting feature of MHRP is that each character has Milestones which are loosely-described events that differ for each PC (eg Nightcrawler has one involving romance; Wolverine has one that involves meeting old enemies and friends) and which - when triggered - allow the character to earn XP. So the player has an incentive to either generate these events, or to respond to situations by reference to their Milestones (eg in the next session, when Wolverine bumped into the others in a Clan Yashida skyscraper in Tokyo, and then defeated a ninja there, Wolvie's player established that the ninja was an old enemy of his with whom he'd crossed paths before).
This means that the GM doesn't have to do the same sort of framing work as in eg Burning Wheel to make sure that the PCs' dramatic needs can be engaged. (Which fits with the comic convention that it doesn't really matter, thematically, whether the X-Men are fighting Dr Doom or Arcade.) It also means that play will typically be lighter and less demanding than (say) Burning Wheel.
It's a good system if you can still find a copy.