The President is at the head of the executive branch of the federal government; his role is to enforce national law as given in the Constitution and written by Congress.
Obama is more than qualified and holds more experience in Constitutional law then anyone on the ticket. Graduating from Havard Law - Practicing + Teaching Civil Rights and Constitutional Law

President as commander-in-chief of the armed forces
Obama has already stated he would work with Generals on the front to pursue actions; he has stated he would like to make a time line for troop with drawl and Bush is now coming around to this. He has also stated he thinks we need to refocus on what the war was supposed to be about and focus on Afghanistan.

power to sign into law or veto bills passed by both houses of Congress
Anyone can do this but being check with current economic details and will of the people is what matters. The past 4 years haven't been very fruitful b/c of a breakdown between the white house and opposition in the house. Obama will be able to make the most change due to the fact of support in congress.

The President also has the power to create a cabinet of advisers and to grant pardons or reprieves.
I think his VP choice says for the type of cabinet he would chose. He chose VP that was qualified and has a good record over choosing someone for strategy to win votes.

President is empowered to make treaties and appoint federal officers, ambassadors, and federal judges, including Justices of the Supreme Court.
This is probably one of the most important and we need a democrat before the republicans take away our RIGHT TO CHOOSE.