Having read Caesar's Gallic War, I will say that this is a better work. Jimenez spends a great deal of time showing inaccuracies in Caesar's commentaries and adds clarification through other sources including archeology. There is a preponderance on Britain, but the book is excellent.
Caesar was a controversial figure. Jimenez argues that he was a mixture of skill and luck. While Jimenez comments on most of the Gallic War and Caesar's Civil War, the main thrust is examining Caesar as an author. In this case, Jimenez sets a simple argument that the Gallic War was a piece of propaganda literature intending to sway public opinion in Rome to support Caesar's controversies.
The strongest point of contention to support this thesis is Caesar's two invasions of Britain, which Jimenez, and most other historians, regard as useless endeavors. In fact, Jimenez goes further to say that Caesar's luck was the only thing that saved him both times. Weather conditions and failing to locate a protective harbor threatened to doom both expeditions. However, Caesar mentions the invasions because Britain was so remote that it was almost mythical to the Romans. His "conquest" added to his public relations persona.
There is also more archeology in Britain from which Jimenez can identify to support his assertions. Using sources other than Caesar himself, notably the letters of Cicero, Jimenez can locate key inconsistencies in the Gallic War, such as Caesar's flight from the Thames to his coastal base because of a Celtic attack in that area. Caesar left the bulk of his armies behind him. However, in the Gallic War, he barely mentions the attack, which his general had repelled by the time Caesar arrived with reinforcements.
The last three chapters in the book continue the thesis of propaganda. Jimenez barely examines the Civil War. His purpose is to show that Caesar continued describing his conquests up until he consolidated Egypt. Jimenez uses other sources to illustrate that the Roman world was fracturing, but Caesar decided to stay with Cleopatra for several more crucial months instead of strengthening his position. At this point, Caesar abruptly ends his writings. He leaves out the part of his dictatorship in Rome.
The last two chapters focus on historiography, especially with regards to Britain. Jimenez points to Medieval sources that confuse Caesar's invasions and distort them. He also presents Welsh mythology as being more accurate than official histories. Archeology more accurately corrected record; but not until the 1800s.
I am disappointed that there was not more analysis of Caesar's interactions with the Celts, especially governance and colonization. Caesar must have been extremely antagonistic towards even allied tribes. The Aedui, who were allies of Rome long before Caesar, and who aided him in his early campaigns in Gaul, eventually turned against him. Most Celtic allies turned against Rome and especially Caesar. There is no clear reason for this, and the omissions are curious. There was virtually no economic discussion in the book. Taxes must have been levied; but Jimenez simply says Caesar stripped Gaul of all of its wealth and gold. For many years after Caesar, they did not mint gold coins. This makes Caesar appear similar to Spanish conquistadors. However, Jimenez simply does not discuss it.
Overall, it is a fascinating look at Caesar. The book is more Caesar and less Celts, and even less Caesar and the Celts. Jimenez is a skilled author and abbreviates Caesar's dry statistics while correcting the chronology, so readers have a greater appreciation of the order of major events.