I will admit at the start that I am not smart enough to read this book. That said, I do think Plantinga is definitely on to something with his idea of Warrant. Unfortunately, this book hardly does it justice.
Plantinga is certain that Warrant is the fountainhead of knowledge, and that is fine, because he is writing the book, but he hardly does a good job of distinguishing this with the common idea of justification. In fact, through the whole book the reader is somewhat confused by what Plantinga means by justification and by warrant, as well. Plantinga doesn't seem to reject justificatory principles in epistemic wholeness, or what have you, but at the same time he doesn't seem to adhere to them either.
Instead of tackling this problem head on, what you find is a rather lengthy diatribe of fellow epistemologists who Plantinga finds displeasing. He could argue for his case much better by simply stating clearly what he thinks justification is, what he thinks warrant is, and why justification does not fit the bill for warrant, and further where justification does fit into our noetic structure. But what we find is a book full of Plantinga complaining about other epistemologists.
And this may be enlightening if in fact Plantinga actually evolved during the book to progress his arguments further. Instead what we find is the same trick used in ever single chapter, and just about on every single page. Take one epistemologists ideas about warrant and apply them to some impossible scenario that hardly makes any sense, and then determine that according to this persons understanding these impossible scenarios do in fact generate warrant for a person. Thus, the whole book is Plantinga calling every epistemologist guilty of almost a conspiracy of ad absurdum.
I would not recommend this book, and in fact I am sorry I read it myself. It seems to have little to do with Plantinga's main argument, which is found in the second book of this series. As I understand it, the Warrant series is an authority for any sense of rational epistemology, and I look forward to truly being able to understand it and take to heart its meaning. I only wish Plantinga could step down to the level of people who could still learn a great deal from him, who do not have the technical prowess his clearly possesses. That said, do not waste your time. Start with Warrant and Proper Function.