Positive Psychology has three pillars:
Positive traits – especially strengths and virtues, but also abilities
Positive institutions – democracy, strong families, free inquiry
Positive psychology has to make a case for positive emotions because they are arguing with Freudians, who say that our achievements and creativity are driven by channeling negative emotions. Seligman argues, probably too emphatically, that "there is not a shred of evidence that strength and virtue are derived from negative motivation." This is mostly an intra-psych squabble about how important and fleeting emotions are.
The strength of positive psychology, in my view, is its attempt to reconnect the psychologists' "traits" with the philosophers' and religious leaders' "virtues." The empirical work that positive psychology builds on is best when it shows how habits of action produce our long-term gratifications and troubles. My favorite sentence on the ambition of Seligman's movement is this: "we need a psychology of rising to the occasion."
The part I am most interested, as I try to construct a positive sociology, is his claim that the third pillar is positive institutions. I think he makes a suggestive beginning in this book in connecting positive character with positive institutions. Most of this work, though, remains to be done. And nearly all of it, I think, is beyond the tools of psychology.