I've designed a super hero game, that for now I'm calling Forces, that I hope approaches the genre from a new lite. Its very narrativistic and structured, but focuses less on a few all encompassing themes and tries instead to highlight the thematic nature of individual characters, especially when working within a team.
The game system began one day after reading some of Grant Morrison's run on JLA and thinking about what exactly made Batman Batman. One of the main things, if you think about it, is his villains: that common thread of duality, insanity and crime that links them together. Other characters have similar features. Spiderman, for instance, is Spiderman only when he fails despite his best efforts, but still fights. A Spiderman enemy is someone who was once Spiderman's friend. Take away these elements and you might be left with a guy that has some cool powers, but your not really talking about the same character.
Now in most games, these kinds of things are left up to the GM, but in Forces, its the player who builds their character's themes, and the players as a group who dictate the tides of the game.
If anyone's interested PM me and I'll send out a early rules draft on as a word file.

You're totally right. This sounds like a really interesting concept. I'm wondering, though, if the same is true for heroes who are part of teams or is this just an aspect of a solo-hero. I know Batman is part of the JLA and Spider-man is now an Avenger, but does that amount of depth of theme require a "solo" title as well?
If I think about Storm or Powergirl, I can only think of villains related to their "team concept", as opposed to their "character concept". Wolverine has his own list of Weapon-X enemies, but he has his own title from time to time.
If there room for a "team theme" in addition to a "character theme?"
I love your observation, and I think it has great possibilities for enriching a game.