This was educational (somewhat), humorous (particularly in the bathroom humor department, be warned), and entertaining, but it's really much more of a satire on manga than ever it is a how-to manual, although it does offer a surprising number of tips and suggestions.
Under the guise of explaining how easy it is to draw manga, the two authors/artists offer a commentary on the state of Japanese manga, what motivates it, and which trends are hot and cold, taking potshots at everything out there, including themselves. The line-drawing artwork is pretty decent and quite varied, and some of the stories they tell are pretty amusing. There is a distinct tendency towards bathroom humor and there is some quite explicit nudity depicted, so this isn't the book you want to give young children who may be displaying a flare for, or an interest in, comic book illustration.
That said I found it amusing and interesting and I'd recommend it for anyone who has a broad mind and is interested in manga.