When one begins learning how to play chess they start by learning the basic tactical motifs, some basic end games and some positional understanding (which comes with the appreciation of studying games). After all of this, one begins constructing an opening repertoire. When a student of mine just learned some basics and was asking me about how to construct an opening repertoire, I told my student that he should consider playing an opening where he can expand on later as he progresses by adding new lines and/or variations so that he won't be bored by chess and still able to use his previous experience from his last opening. So openings like the Slav and the Semi-Slav work well together because you will still have experience from playing the Exchange variation of the Slav if you move on from the Slav to the Semi-Slav. King's Indian is also very rich when comes to choosing new variations to play. French Defence is another good opening with a lot of varied different positions. Basically, all sound openings as Black are sound and have a varied scope.
So what does this have to do with this book? Because John Cox's repertoire is at it's best if you play the Nimzo move-order. In fact, this repertoire is centered around the Tartakower which you will be able to see far more often with the Nimzo move order than the 3. ... Be7 move order (which will take you to the Exchange variation far more often than the Nimzo move order). But let's say you start crashing into players who answer 1. d4 Nf6 2. c4 e6 with 3. Nc3! If you play 3. ... d5 you will have to play the Exchange variation with Nf6 which Cox covers, but this move order proposed by Mr. Cox should encourage you to start playing the Nimzo Indian in the near future.
As far as content, after reading the book, I would feel very comfortable playing all of John Cox's recommendations. Against the Exchange variation John Cox makes an attempt to revive a variation of the QGD which has been considered by modern theory to be "refuted." Cox annotates Kasparov vs. Andersson Reykjavik 1988 in detail and proposes many improvements for the Black side. Though the game between Kasparov and Andersson was a one-sided slaughter, Cox's confidence in his analysis should give the reader hope. Otherwise the reader could take up Nigel Short's "cheeky move order" and play a Queenless middle game in which Black has the Bishop pair and doubled f-pawns.
Against the Classical set-up, Cox only covers the Tartakower and the Lasker. No Orthodox Defense here. I personally find that the Tartakower is a very good choice for a repertoire but it might be too positionally demanding for an inexperienced player. The positions that arise in the Tartakower gives Black a lot of piece play but also a very loose pawn structure prone to attack. However, the Tartakower is still very logical and is still a good way to teach a beginner the hows and whys of both sides and their struggle over the e4 and d5 squares. In order to play the Tartakower properly, beginners and players who are taking up the QGD for the first time should consult Matthew Sadler's fantastic "Queen's Gambit Declined."
The Lasker Defence is another choice I like quite a lot. I have always felt that the Lasker is an evolutionary improvement over the Orthodox Defence. However, like my advice above, in order to understand these systems one should consult Matthew Sadler's book for a strategic overview.
And have I stressed about the importance of Matthew Sadler's book on the Queen's Gambit Declined? Indeed I have. Understanding how to use a gun is important, but what good is a gun without ammunition? You should consider reading Matthew Sadler's book first before even getting a repertoire book or a theoretical tome on the QGD. And when you get Matthew Sadler's book, I would recommend you start reading the section on the Orthodox right away before choosing whether you wish to start up playing the Tartakower or Lasker. Understanding the Orthodox helps the player on the Black side appreciate the nuances, strategic improvements and weaknesses of the Tartakower and Lasker. Of course, with Sadler's book, if you're already an experienced player and makes frequent use of a database, this book might be all that you would need.
And another line I would like to comment on is John Cox's theoretical update on the Bf4 line in the Three Knights QGD. He brings the Black player up to speed with new games and analysis in this "hot amongst the elite" line.
John Cox as a chess author has produced nothing but good books in the past and has became a must-buy for me whenever any of his books come out. Fortunately, I use all of his books except his Starting Out: 1. d4 which I do not have seeing as I am not interested in his repertoire for White. The books I do use are his 1. d4 Deviations, Berlin Wall and this book. And like the other mentioned books, John Cox has a sense of humor in which he willingly shares with his readers. For example, John Cox shows you many variations where Black gets good play but ends up in slightly unbalanced but still sterile positions. John Cox likes to believe that his primary audience would be what he also happens to call them, "nihilists." As I go through this book and his book on the Berlin I can't help but chuckle to myself whenever he eerily gives variations that lead to sterility.
Overall, I think this book is worth your money and is easily a labor of love. And for $20 (retail is $26-28 I think), I find this book to be quite a steal. Also, unlike the other Everyman books, the binding on this book will not fall apart on you.