From a literary and mythological standpoint, I can't imagine anything worse than writing down the New Testament. One of the key features of ancient mythology was that it developed and evolved as it was told and retold over generations. Those parts which were compelling, interesting, and original tended to be retold more than those parts which were uninteresting, boring, or unfavorable. The result were tales which were rich and wonderful, developing the basis for modern fiction. Themes of love and loss and bravery and sacrifice were explored and honed until the best parts were all that remained.
The New Testament of the Christian Bible, despite having been interpreted slightly differently as it's translated into different languages, has remained basically the same for a millennium. While some people try to extrapolate on the source material with their own interpretations of things they see as vague, the source material is the same. What would the stories of Christian mythology be like had they been handed down from generation to generation through stories instead of stale and unchanging print? Could the religion have adapted better, allowing for quicker scientific and social progress? Could it have prevented wars and cruelty? Or could it have enabled greater horrors than we could imagine?
If it were told by word of mouth stories we would probably have even more sects of Christianity, perhaps even more religions branched from it.
If Christianity had evolved through word of mouth stories and fables rather than being written, it would be the worst game of telephone in history, that's for sure. It would be like fishing tales.