Making Comics is an excellent book for anyone who is interested in making comics, or just learning about the theory behind them.
Scott McCloud lays out the fundamental building blocks and questions behind creating a comic, and covers them in depth. He eschews questions of technical execution and personal style in favor of theory and design.
He covers communication, pacing, framing, and transitions in excellent detail. His chapter on the tools available is more brief, but gives a beginning cartoonist enough information to help decide where they would like to make their first forays.
The chapters on words and writing are similar to those on art. Rather than a step-by-step manual on how to do it, he presents the groundwork on what to do, and how to approach it.
Throughout the book, the focus stays steadily on the comics medium. Art and words, working together to tell stories. This single-minded focus makes the book more valuable to a comic artist than a more general treatise on art of creative writing.
Along with his earlier work, Understanding Comics: The Invisible Art, Making Comics is an excellent resource for understanding or creating your own comics masterpiece. McCloud also offers some supplemental material on his website for free.
As an aside, the book also clued me in to some other, non-mainstream comics work that I am already enjoying checking out.