World bank would be a success if you are measuring in terms of money; however, it would be very harmful to people of smaller countries who have their own way of doing things and do not need to keep up with the finances of master nations. It is important to keep all countries afloat as much as possible. This cannot be done unless each country maintains their own banking system.
A world bank would be a success provided that the entire planet used one currency. We aren't there yet, but things are moving in that direction. When there is one currency, there are no exchange rates and interest rates on loans would be more clearly defined. However, many of the world's economies are too disparate in order to have one currency at the moment.
World bank would be a failure. I believe this because if you examine the history of world bank they have made some pretty poor choices when it comes to spending our money. World bank has done almost nothing with the billions that it was given to save our rain forests. They have made some other epic failures in the past and I think they will continue making bad decisions.
A world bank would be a failure because there would be to many hands in the cookie jar. To many countries would have conflicting ideas of what to do during recessions and other pressing times. This would eventually lead to the failure of a world bank. I think the current system is better.
A world bank would not be a success for the same reason that the European bank has not been a success. Different countries have different types of economies, and they need to set different interest rates. If a single bank had the same rates for the whole world, it would cause a situation like the one in Europe.