Grant Morrison, the writer of classic graphic novels such as Arkham Asylum, has the best ideas-to-page ratio of any contemporary author (according to my nephew).
In Supergods he applies his expertise and deep knowledge of the history of superhero comics to create a fascinating narrative of how the superhero has evolved, from the Golden Age of the early Superman and Batman stories, through the Silver Age of Marvel Comics' heyday, to the cynical and sadistic turn comics took in the Dark Age of the 1980s and 1990s, and through to the contemporary renaissance of comic books in which Morrison himself has played a leading role.
As he points out, each age gets the superheroes it requires, whether champions of the oppressed, patriots, rebels or conformists. His analysis is acute and often witty; I loved his characterisation of Batman as the Rolling Stones to Superman's Beatles. The middle section of the book focuses more on Morrison's own personal journey as a writer, and a long section about a drug-induced epiphany in Kathmandu in which he perceived the interconnectedness of all living things had me flipping the pages impatiently; mystical experiences, like dreams, are more interesting to have than to hear about.
But Morrison's central thesis, that we need superhero stories because they "contain at their hearts all the hopes and fears of generations in vivid miniature" is amply demonstrated, and this book has made me eager to rediscover the world of superhero comics, which I have not visited since my teens.