BTW, here is another really interesting book which analyzes the comic/manga medium from an artistic perspective:
Scott McCloud, Understanding Comics
Scott McCloud's "Understanding Comics," a creation that sits roughly between comic book and historical literary criticism, is an indispensable work for anyone interested in studying funnybooks seriously. Along with Will Eisner's seminal works on the subject (which I have not read all the way through), "Understanding Comics" uses the graphic-text art form to dissect one of the most rapidly growing trends in both art and literature. In an accessible, readable style, McCloud takes the reader through the history of comics, the definition of comics as a sequential art form involving symbols, and examines several major trends in modern comic-dom.
While there's plenty here for both the casual reader and someone interested in more scholarly study. While it's more of an introduction than an in-depth exploration of comic study, McCloud provides enough resources for someone to continue study on his or her own, and enough seeds to begin sprouting ideas about the funnybooks. Occasionally, he misses the mark - his definition of art, for example, is a little broad - and "Understanding Comics" isn't nearly as well-cited as it could be, but these are easily overlooked flaws.
Especially beneficial is his comparison of Japanese Manga comics with traditional American graphic storytelling, because the two are basically the same medium but evolved almost entirely independent of each other, until the last 15 years or so. I wouldn't recommend it for the Sailor Moon fans, but those that enjoy anime and Manga will find much useful information here, in particular the comparisons between the two comic forms (not so much in any actual study of Manga in and of itself).
I highly recommend "Understanding Comics" to anyone who wants to - well - understand comics. Whether you are interested in the ways Alan Moore tells a story, or want to deconstruct the use of movement in Dave McKean's artwork, or you want to learn why Spiegelman chose certain symbols and styles in his work, "Understanding Comics" gives the reader an excellent springboard to further study.