A very interesting book, this one... Marcus Borg (about as liberal as a Christian can get, if not more so) and NT Wright (fairly conservative) discuss who Jesus was/is, who he thought he was, what he did, etc
In general, Borg takes the line that Jesus was a man (but not God) who in some sense after his death became "the Christ of faith", and that most of the gospel accounts are actually metaphors written back into the life of Jesus by the early church. This includes basically most of his teaching, miracles, birth, resurrection, etc. Wright takes a much more normal line - that Jesus was the Messiah, claiming to bring about God's kingdom and the true return from exile, that he was born of a virgin, raised from the dead, etc. He doesn't exactly follow the standard evangelical line, but I'd agree with everything he said, even though sometimes there's more to say as well. But you can't talk exhaustively about Jesus in one non especially large book.
What I found most interesting about the book was the difference in approach taken by Borg and Wright. Borg's liberal position is the one that traditionally is seen as more "scientific", but time and again the only arguments he uses for his position are "I think that..." and "It looks suspect to me...". They're almost all subjective. By contrast, Wright's approach is heavily evidence-based, looking at how first century Jews would have understood what Jesus was doing, examining evidence for how oral tradition works, etc.
It's also interesting looking at Borg's presuppositions - some of them are fairly clear in what he writes. He presupposes, for example, that God doesn't or can't act in the world, as he cannot see any explanation for the Holocaust otherwise. But his argument then hinges upon Jesus as a mystic, who experienced God within the world. If God cannot or does not act in the world, we cannot experience him in the world. Borg's approach is logically inconsistent.
Another example would be Borg's assumption that if something has a metaphorical meaning as well as a literal meaning, it was probably written only because the metaphorical meaning was true, rather than both being true. So, for example, Jesus riding into Jerusalem on a donkey fulfils promises about what God's king would do from hundreds of years before. So Borg seems to argue that the early Christians saw Jesus as God's king, so wrote that he had fulfilled this prophecy (even though he hadn't) as a way of pointing to his identity. Which does rather raise the question, as Wright points out, of how on earth they came to believe that Jesus was God's king if he didn't fulfil the prophecy.
Borg also makes strange assumptions which almost seem designed to reinforce his position. For example, he assumes that if three gospels carry very similar stories, that one of them was written first, that the other two copied the story and made up their extra details, only leaving one source. Which makes me wonder then how anything could ever be attested by more than one source...
In some circles, the controversy over this book was because Wright acknowledges that Borg is a Christian. I don't know Borg; Tom Wright does. I'm glad it's God making the call, not me.
All in all, an interesting read and a good introduction to the whole "historical Jesus" debate. Whether that debate is worth bothering with, except to refute the sceptics, is a different question altogether.