Rohani campaigned on a platform of moderating the current extremist government policies, and the people responded to that. Of course, this does not mean the Iranian government will immediately change their current policies (since the real power rests with Ayatollah Khamenei). But it does bode well for the future. Rohani is now in a position to exert a moderating influence on Khamenei, and it is clear that most Iranians would like to see more moderate policies from their government.
This does not solve all of our problems with Iran. But Iran has taken a small step toward moderation, and it might be time for the U.S. and other western nations to respond to that by also showing a bit more moderation. The last thing either nation needs is a war, and this should be viewed as an enhanced opportunity for a negotiated settlement of differences.