This book isn’t meant to be a biblical account, as in based on the Christian Bible. What is does is, use the Christian Bible as a base and wrap it with other historical accounts from the time period. Such as lifestyles and personalities of leaders, and key figures, information the Bible doesn’t record in detail. It also brings to the forefront the politics of the day within the Roman Empire and the state of Judea.
For the reader there’s more context around the Judaism of that time period and the workings of the second Jewish Temple, the good, the bad, and the ugly. This book functions as neither and both, a religious and historical book. It was a rare joining of perspectives.
The complaints I’ve read about the book are sometimes along the lines of “too much history about the Roman Empire.” If you want a 100% Jesus book, this isn’t for you. You will either like it or have no interest.