I think it was a good book to show another point of view about Jesus' story and the Church through a nice and neutral story. It would be stupid though if now who is Christian changes his believes. Personally, not believing in the Bible, i don't believe in that nice tale either, but i cannot say that it's only fiction, and i guess nobody will, because if this thing is real and still carried on, they'll leave people wonder, and if it's not real they'll leave people wonder anyways because it's moving the mass and so creating business.
I agree the characters sucked, he could have done better. Same thing in Angels and Demons. I enjoyed reading both books though.