I've been off work sick the last few days and conveniently my copy of the 13th Age core book arrived in the middle of it so I have taken the opportunity to read most of the rules, and skim the monsters and class options. Overall I really like the look of this game and would like to play it, but this isn‘t a review.
What I want to talk about here is what I consider the most useful thought technology introduced in the game: opt-in player responsibility, both for complexity and story development.
For complexity, the game provides an ordering of classes (pg 75) by Ease of Play, and for each class presents play style information to guide players towards choices that suit their interests. Individual classes also provide various options for play to fine tune this. While earlier editions of the D&D (though notably not 4e) have always provided classes of different complexity, the way they are presented in 13th Age make it clear that this is a feature the designers intended.
While the mechanical complexity is important, I think the options around story development is more so. What I mean by story development is how much individual players take on responsibility for working with the GM to author the story. In a ‘traditional’ game this is solely the GM’s responsibility with players domains being limited to their characters. 13th Age however has a foot in the ‘story game‘ world too where players take a strong hand in the story. Opting to let players find their own levels of involvement with story generation allows the game to cater to groups with mixed interest in this style of play.
This is not to say this innovation is more important than say Icons, or One Unique Thing. Simply that by considering player options like this and being explicit about calling them out the game is better suited to introduce it‘s more dramatic ideas to a traditional group.