From the book jacket:
From one of the most acclaimed and profound writers in the world of comics comes a thrilling and provocative exploration of humankind’s great modern myth: the superhero
The first superhero comic ever published, Action Comics no. 1 in 1938, introduced the world to something both unprecedented and timeless: Superman, a caped god for the modern age. In a matter of years, the skies of the imaginary world were filled with strange mutants, aliens, and vigilantes: Batman, Wonder Woman, the Fantastic Four, Iron Man, and the X-Men—the list of names as familiar as our own. In less than a century, they’ve gone from not existing at all to being everywhere we look: on our movie and television screens, in our videogames and dreams. But what are they trying to tell us?
For Grant Morrison, arguably the greatest of contemporary chroniclers of the “superworld,” these heroes are powerful archetypes whose ongoing, decades-spanning story arcs reflect and predict the course of human existence: Through them we tell the story of ourselves, our troubled history, and our starry aspirations. In this exhilarating work of a lifetime, Morrison draws on art, science, mythology, and his own astonishing journeys through this shadow universe to provide the first true history of the superhero—why they matter, why they will always be with us, and what they tell us about who we are . . . and what we may yet become.
Here is a conversation between Morrison and Neil Gaiman from EW and a discussion of the book on NPR.
Even if you don't like this type of fiction, I suggest that every librarian who works with leisure readers at least skims this book. It will really give you a good understanding of why these books appeal to readers.
I have a hold on this book and will post a review after I read it.
In the meantime, other books about genre fiction that I would highly suggest you read as a training exercise are Dangerous Men and Adventurous Women: Romance Writers on the Appeal of the Romance (New Cultural Studies) edited by Jayne Ann Krentz and Maps and Legends: Reading and Writing Along the Borderlands by Michael Chabon. The former is a "suggested" reading in my RA class and the later is required reading (well, at least the chapter entitled "Trickster in a Suit of Lights" is).