I think what Atwill did really well was to create an understanding of the Gospels as a whole unit, and not a collection of disparate pieces. Scholars have long debated the meaning of the differences between the Gospel tales, and have tried to tease understanding from their respective lacunae. Atwill demonstrates several times that these gaps and textual conflicts were inserted on purpose in order to achieve specific results. Sometimes this was to indicate that there were more than one character with the same name. Other times, the effect was to highlight puzzles hidden in the text. And it is these puzzles that bring out the messages that were presumably embedded to benefit the Flavians.
The key to understanding the New Testament, according to Atwill, is Josephus' "Wars of the Jews". The "history" created by Josephus is our only window on what happened in 1st Century Judea, and it primarily centers upon the actions of the Romans in their conquest. Atwill found that Josephus' description of Titus' campaign, through the siege and destruction of Jerusalem and Masada, was perfectly reflected in the ministry of Jesus in both chronology and character. Many stories only partially relayed by the New Testament were completed in "Wars of the Jews", and most of the puzzles required a careful reading of both the New Testament and "Wars of the Jews".
The resurrection scene in the New Testament -- that point when the disciples discover the tomb of Jesus is empty -- has caused many debates because each book relates a slightly different tale. People arrive in different orders, at different times, and have different encounters depending on which book is read. Atwill uses the time clues in each story to create a single, coherent story. In the process, he discovers the humor intentionally implanted there. First, it become obvious that the tomb Mary first discovers wasn't Jesus' tomb, but the one for Lazarus! Then, as each set of followers appear at the tomb, another set encounters the last and assumes them to the 'angels'. This comedy of errors continues on through all four books and results in the recognition of a key point: there were several messiahs active at the same time -- several Jesuses! -- and their followers didn't recognize each other.
One persistent target of this Flavian satire is particularly hard to read about: the famine during the siege of Jerusalem. Reports that the inhabitants (with well known eating restrictions) resorted to cannibalism was a continuing joke, all the way up to the proclamation of Jesus that he was "living bread", and that his companions were to "eat of him". The story in "Wars of the Jews" about a woman named Mary who kills and eats her nursing child is used multiple times as the basis for a number of jokes in the Gospels. Even the "resurrection" of Lazarus is shown to be another reference to cannibalism.
Atwill comes up with several reasons behind the invention of Christianity, and specifically about why certain elements exist in the New Testament. Primarily, the purpose was to co-opt the militaristic Messiah cult popular at the time, replacing it with a passive, stoic cult more amenable to Roman interests. Secondarily, they wanted a cult that would be attractive to the illiterate underclasses while being obvious satire for the patrician class. Titus wanted folks to mock and hate the Jews, and he wanted to trick the "true believer" Messiah cultists into worshiping him as Christ. Crucially, these works together were key in promoting his dad, Vespasian, as divine so that the Roman Senate would confirm Vespasian as a God. There was, in short, a lot of heavy lifting Titus expected from these works; more to the point, he got a lot out of them.
It is in the last quarter of the book that Atwill really shines. He comes out with an understanding about how the Maccabees fit into the history of the Jewish rebellion, and thus in the Gospels -- also explaining why there are so many people in the Gospels with the same half-dozen names. He breaks out the crucial components of the Jesus story to show which parts derived from the popular messiah cult, which came from Flavian preferences, and which were recycled truisms and prophecies from prior messiahs and prophets. He names the people involved in the creation of Christianity. He explains the mechanic for how the Early Church was formed in the Seven Cities of Asia -- alongside the Imperial cult! He also reviews the dates provided by Josephus in his "Wars of the Jews" and determines that most, if not all, the dating within is highly suspect, as Josephus was far more concerned with matching prophecies from Daniel than having a quotidian fixation on correct dates.
Although I was shocked and surprised by many of the assertions made in this book, I never found myself disagreeing with Atwill's understanding of history. He repeatedly makes his point using nearly every verse in the Gospels, and drags the reader through a series of conflicts in the texts, along with their resolution. I think this would be a difficult book for a practicing Christian to read and an impossible book for a biblical literalist to comprehend. Even I found the book to be troubling in its expose of just how much of the cruelty and evil inherent to Christianity was there on purpose. Accepting what Atwill says is challenging and disruptive, but I'm afraid that arguing against his points would be a much more difficult challenge.
Now I understand why the major media went out of their way to vilify Atwill and confuse his points. This is a dark, dangerous book that I would only recommend to my friends interested in history or Western occultism, because, frankly, I don't expect that anyone else would be able to cope with it.