This book is not a history of religion in general but specifically a
(sometimes wild) speculation on how the monotheistic god of the Jews, of the
Christians and of the Muslims came to be.
There is little or no background about preexisting religions, and virtually
no analysis of preexisting monotheistic beliefs (in particular, the one that
obviously influenced Judaism: Zoroastrianism).
This book makes for an interesting commentary to the Bible if you are the kind
inclined to read the Bible at night. As far as history, much better books
have been written by specialists in Jewish history.
The chapters that debunk the story of Jesus sound naive and poorly informed.
Wright only studied a small percentage of the books written on the historical
Jesus (see this page).
As usual, the debunking of the Quran is much much milder than the one of the Gospels (one religion beheads you, the other one doesn't). There would be much more to say about the historical Islam (see this page).
The last chapters are devoted to the "clash of civilization" that was popular after the 2001 terrorist attacks. Wright turns into a philosopher arguing that the USA needs to understand the reasons of the terrorists in order to win the war against them. And the book concludes with an even more philosophical discussion of what "God" means. Wright sees a moral order in the world, created by the evolutionary history of the human species. To him the scriptures simply reflect that moral order and impose punishment on those who break it. His conclusion is that "God" is simply another word for "love". He basically turns things around: instead of monotheistic religion having created morality for the masses, religion has simply encloded a morality that preexisted. This sounds like old-fashioned new-age philosophy. He hardly spends a page discussing the history the human civilization. We have to take for granted that there is such a moral order without any proof of it. He also implies that there has been constant progress towards morality. Europeans probably beg to disagree, after a century of massacres (two world wars, Hitler Stalin, not to mention the slave trade and colonialism of the previous century). Nor can the Japanese be too happy that 2,000 years of history culminated with the atomic bombs on Hiroshima and Nagasaki. Wright is simply projecting the state of the world in which he lives: after the end of the Cold War, this is largely a world at peace. But there have been periods of peace before, usually when an empire dominated so totally that major wars were unthinkable (Roman empire, Mongol empire, British empire). Unfortunately, each of them eventually dissipated and evil reappeared (with a vengeance). Good luck to Wright's children.
Many of Wright's statements about the Jewish, Christian and Muslim scriptures are pure speculation, of the kind that abounds in Hollywood movies. So take this book with a grain of salt.