I recently finished this and thought I would draw a little attention to it. Part skim-history and contextualisation of trends of US comic book superheroes (with an emphasis on DC and Marvel), and part memoir of Morrison's life reflected through his involvement with comic books as reader and later creator, Supergods was something I found very entertaining.
There is inherent bias in the book; this is no purely subjective work. Morrison as a figure becomes strongly placed within the text as the historical aspect catches up with his own life-time, and so his viewpoint is conveyed within his writing and has to be taken for what it is: one commentator's viewpoint. But that is to miss the point of course.
I am not a slavish fan of Grant Morrison's work, and do not enjoy everything he does, but what I do enjoy is that he is a writer of 'big ideas' and is always looking to incorporate them into his work, whether science, philosophy, religion, culture, media, life, death, love or whatever, it finds its way into his work over the decades.
I would recommend Supergods to anyone who likes at least some of Grant Morrison's work and is looking for a read about comics that is no dry history of the subject.