S!

On the topic of under-appreciated books about supermen...

 Some people find Superman boring because he's invulnerable, but he's not, of course. He cares, which makes him extremely vulnerable. Elliot S. (later S!) Maggin's "Superman, Last Son of Krypton" – originally published in 1977 to accompany the release of the Motion Picture – was happily brought to my attention by Colin Smith here (with surprise input from S! himself in the comments below: "Of course Alan Moore read my book"). Reading nothing like a novelization – more like a very early Kurt Vonnegut – the book is careful and witty and full of aliens. One of my favourite paragraphs is the opening of Chapter 6 "The Penthouse", a beautiful and unfamiliar introduction to an archetypal megalomaniac:

"Yesterday Luthor was dressed in skin-tight pyjamas and crossed ammunition belts. The outfit was the only affectation he had for a purpose, and therefore the only one he recognized as an affectation. The penthouse hideaway four hundred feet over the city, the medieval tapestries hanging over the faces of the computers and wall consoles, the Egyptian sarcophagus whose mummy was replaced by a mattress covered with Snoopy sheets and pillowcases, paintings on the walls by Leyendecker, Peake, Frazetta and Adams, those weren't affectations. Those were matters of taste. Luthor was flying in the terrace window with his jet boots for the seventeenth time and he was running out of videotape."