If there was already a predetermined agreement between two countries and it is resulting in positive consequences, then new leaders should respect this agreement as they are not experienced in the situation and may not know all of the facts and ultimately causing a disruption in relations or government rulings.
Mr. Trump should honor President Obama's agreement with Iran. If for no other reason than he is just beginning to get into the complexities of the situation. Until Mr. Trump can better understand what has come before him, he should continue on the current path. Then when he is fully immersed in the situation he can consider alternatives.
Trump has big shoes to fill in Obama's place. I fear that many of his decisions will not fare well for the US (Or us here in Canada for that matter). By dishonoring that agreement he will only damage the credibility of the US. There is also a possibility for retaliation. It is important to uphold one's word. Especially on the scale of a national agreement.
There were many people that criticized Obama's agreement with Iran when it went into place. The agreement more or less gave Iran access to nuclear weapons with very little oversight from the United States and other countries. Trump should not honor it because it might be the only chance to stop Iran from making nuclear weapons.