Well, I haven't read this work and looking at a bit of reader reviews at amazon it looks as if it would be etnertaining, but not exactly what I would grab next.
What are you really hoping to read about? The gospels in context, within the environment that they were produced? Just New Testament material? Gnosticism?
An overview of what scholars think about the texts?
As an introductory volume of a general New Testament quest I can recommend Burton Mack's "Who Wrote the New Testament? : The Making of the Christian Myth" is an interesting starting point, will make you think, will help you to find a vantage point to look further into one side of the coin or another.
I have found Michael Grant's books on Paul and on Jesus to also be interesting to begin an inquiry. . . they'll give you a historical perspective that sums up a traditional historian's attitude up to the middle of the last century or so. Another good book along these lines is "Bandits, Prophets, and Messiahs: Popular Movements in the Time of Jesus" by Richard A. Horsley, John S. Hanson. Quite good overview of the diversity of political and religious thought around the time of Jesus.
If you're interested in Gnosticism, Jonas' and Rudolph's books are the best primers, and I really like what Elaine Pagels has written about Christian Gnosticism in "The Gnostic Gospels" and "Beyond Belief," etc.
The book that bowled me over when I read it after reading about a decade's worth of books about christian origins was . . . "The Mythmaker: Paul and the Invention of Christianity" by Hyam Maccoby. POWERFUL . . . it seemed to mirror my own conclusions about Paul and gentile christianity.