The president in Iran has quite limited powers. The Supreme Leader is the man who really decides about questions of foreign affairs. For instance, when an agreement was reached in 2003 to suspend Iran's nuclear activities, the Iranian president at the time was not even informed about this agreement. It was signed by the representative of the Supreme Leader.
So the election of a new president is important primarily as an indication of which direction the Supreme Leader would like things to go. The Supreme Leader has much influence over how the election takes place. He has much influence over the results, the widespread allegations of considerable fraud, but even setting that aside, the Supreme Leader really dictates what kind of coverage there is in the newspapers and especially on television, and this really means that he dictates the results.
Among the three announced candidates besides the current president, I would say that at least two of those candidates have indicated that they think Ahmadinejad's stance is way too provocative and aggressive, but they have not indicated yet if they would change the objective. They would change the tone, but perhaps we should welcome the small step of changing the tone.