This book is almost 50 years old and would be a very poor choice as a lesson-based book to learn Korean from. (For example it predates modern computerized printing of non-Latin alphabets and is all in Yale Romanization and not Hangul.) However it will be of interest to some for the glimpses it offers of Korean two generations removed from what people speak today. For example it devotes much of one of the later chapters to the familiar or hageche speech style and presents a rather humorous dialog entitled The Henpecked Husband that is all in that style. Martin's linguistic treatment of the language in the book is very much in line with that of his later Reference Grammar of Korean (1993), but is aimed at the learner and is generally kept as simple as possible.
The book is all in romanization, which has deterred many potential users, but if understanding the structure of the language is your priority, then this book will help you more than any other.
The exercises were challenging and I had to revise previous chapters quite often. They force you to really think in Korean, and what I realized whilst working with the book is that I actually remember grammar significantly better when I focus on spoken Korean rather written Korean.
Besides the exercises the book has another strength: the depth of grammar it covers. Martin takes you from the very Basics to the Advanced, and in this regard the book is complete. However it is not just the breadth of coverage that impressed me but also the way in which he explains things, he manages to explain rather complex and above all "alien" grammatical structures in a lucid, analytical and logical manner. None of the books I used before really explained how the language "works", why and how it is structured the way it is, in this book Martin does. Things you learn in this book about the language is what other series cover in advanced grammar books.
This is a book for learners who want to go beyond a superficial understanding of how the Korean language is structured, it is a book for people who seek to master spoken Korean, and consequently, master Korean grammar.
Negatives ? The book's rendition of the Yale phonetic system for Korean was not adequate, I advise the future buyer to search the web for decent explanations, which is easy to find.