Let me first clarify the confusion over Sun Wu ("Sun Tzu")'s The Art of War and this book.
This is not a translation of the book The Art of War as it is known by the Western world. Sun Wu, a strategist from hundreds of years before Zhuge Liang, is indeed the father of Chinese military strategy, but culturally Zhuge Liang has acquired an even higher stature. A master strategist in the Three Kingdoms period, Zhuge Liang was dubbed "The Hidden Dragon", one of the two greatest strategists of the time, alongside his colleague Pang Tong ("The Young Phoenix"). Zhuge Liang almost single-handedly turned the wandering warlord Liu Bei, "whose army did not exceed a thousand", into one of the three superpowers during the Chinese civil wars of the Three Kingdoms. Zhuge Liang's reputation for manipulating the enemy was so great that he eventually became known as a sorceror figure who was able to summon weather and conjure spirits to do his bidding. For the record -- Zhuge Liang, philosophically, belonged to the "ru jia", or "confucianism", and *not* taoism or legalism, though often his methodology and concepts show similarities to the latter two. Zhuge Liang belongs in a tradition of "ru zhang", or "confucian generals", military leaders who were learned and studied, skilled in literature and philosophy, yet actively led military campaigns.
His influence has permeated Chinese culture -- in Chinese language, the name "Zhuge Liang" is now used (and not archaically) as a symbol of preternatural intelligence, while if you used "Sun Tzu" in your everyday language, you'd be considered pretentious.
Finally, the very title "The Art of War" has always been misleading. The Chinese term "bing fa" means more along the lines of "the methodology of war", and the use of this term often does *not* refer to the specific title of Sun Wu's treatise; the words "bing fa" are often used in the way you'd use the words "geography", "physics", or "agriculture". The translation "The Art of War" probably puts Sun Wu's original work more in the realm of philosophy than was ever intended -- imagine if a book entitled "Geographical Studies" were translated as "The Art of the Earth".
This particular book is *not* a translation of Sun Wu's "bing fa". It does not pretend to be one: The cover explicitly says that it is "Zhuge Liang's and Liu Ji's commentaries on the classic by Sun Tzu". So those who complain that this is a poor translation of Sun Wu's book need to have their eyesight checked.
That said, I still have major issues with this book.
I've never had the chance to read any of Zhuge Liang's original writings on warfare. Fictitious accounts of his life as related in Romance of the Three Kingdoms mention books that he'd passed onto his military successor Jiang Wei, but I had never found these in the original Chinese language. Thomas Cleary's translated passages in this book read as extremely dry, and far too general. Most of the concepts amount to "Be kind to your men, be smart in dealing with your enemies, don't fight unless victory is sure". All true, of course, but how useful is that? Occasionally interesting angles emerge ("to know an officer, get them drunk to observe their nature"; "a decadence in a general - to assess others without assessing oneself"), but all in all, these translated passages read like proverbs, with broadly defined terms. Not having read the original Chinese text, I don't know whether the problem stems from the original works by Zhuge Liang or from Mr. Cleary's translations, but I do know that the Chinese language, especially passages of discourse, are highly difficult to translate and often come across as broad and imprecise when put into another language. There are so many Chinese words without properly English equivalents (for example "Xiao", which combines filial obedience with love, and "Yi", which means far more than just "honour" or "loyalty" could convey) that Chinese-English translation is always a tricky business.
However, in moving to the second half, the "Liu Ji" section, I find major flaws in Mr. Cleary's work. The right-hand man of Ming Dynasty founder Zhu Yuan Zhang, Liu Ji was another strategist who had acquired near-mystical status; under his familiar name "Liu Ba Wen", Liu Ji is known as a fortune-teller figure who saves Zhu by reading omens and stars. He's not exactly known for military strategy in the same way as Sun Wu or Zhuge Liang, but once I'd figured out who he was, I was quite eager to read the translation.
Much like the approach of Meng Zi ("Mencius"), Liu Ji uses examples and stories to illustrate his points -- which makes his points a livelier read. Unfortunately, here Mr. Cleary's translations are often awkward, bogged down by names and geography. This book was smart in including a timeline of dynasties and Chinese historical periods referred to in Liu Ji's tales, but probably should have included maps from various periods. Many of the warlord states and territories over Chinese history share the same phonetic translation ("Jin", "Han", "Wei", and "Wu" all have multiple, disparate representatives throughout Chinese history), and Mr. Cleary's translations of these tales become very cluttered because of this. I had studied the Warring States and Three Kingdoms periods quite a bit, if not in an academic setting, and even I was usually confused as to when and where I was in a particular tale.
However, Mr. Cleary makes an even greater mistake in certain tales by omitting the names of participants. And when a tale refers to "this general and that governor and that other general...", it's linguistic chaos. As difficult as it may be to know the various phonetically translated names, omitting them not only raises questions as to the translation's faithfulness to the original text, but also discredits such tales on a stylistic level -- without the specificity of characters, the accounts may well have been fictitious (though they're not).
On a very broad level, some of the concepts in this book probably can be applied to the modern day. But there are precious few strategies to be absorbed from here that are detailed and specific enough to prove practically useful. Personally, I had bought this book in hopes of getting a more historical and less mystical picture of the man Zhuge Liang himself, and on that front, this book was entirely wrong for the job. I knew no more about Zhuge Liang after reading this than I had known from growing up in Chinese culture, reading Romance of the Three Kingdoms, and my past historical research into the Three Kingdoms period. So to me, this book is simply a novelty, lacking in the information I needed.