First off, Eisner does a great job of combining visual elements with his text in this book. The whole thing is illustrated with cavemen working on their storytelling technique, and I have to admit that the cavemen illustrations were great fun and always helped to clarify the how side of what he was saying in the text. Beautifully done. (Yes, I know, this is like saying, "Hey, y'know that Hemingway guy? Some of his stories were really good.")
Does it have any issues? Yes. It's 164 heavily illustrated pages. You can read it in an afternoon. And some of the illustrative pieces feel over-long for the point they are trying to prove. I hit the point on a couple of them where I found myself saying, "Yes, I get it. We needed the X in the beginning so we would understand Y now. Can we move on?" I also felt that, at 164 pages, he didn't really have the opportunity to go into depth on some areas. There's a point where he provided two bad examples of a comic script... and no good example. Aaaaah!
Even with those issues in mind, I have to give the book 4 caped crime-fighters out of five. It's well-written (though there are also some grammatical gaffs that make me want to scream), it's engaging, and it's instructive. Worth the read.