America's second president, John Adams, was the first political leader who had to face democratic politics as we know it today, whereas his predecessor, George Washington, enjoyed an unchallenged charismatic authority as the glorious hero of the Revolution. But what Washington won on the battlefield as a general, Adams won at the conference table as a diplomat: a vital loan that helped finance the Revolution and the favorable peace terms of the Treaty of Paris in 1783. As president, Adams dealt with international relations, civil liberties, and domestic rebellion with a keen sense of power, fairness, and justice. He had a better grasp of where America was heading than did Thomas Jefferson, and had it not been for the political institutions Adams defended -- a strong executive, the Supreme Court, the Senate, the military -- America's democratic ideals would have had no means of realization. This is Adam's legacy.John Patrick Diggins, John Adams (American Presidents Series, vol. 2, Times Books: 2003).
I would also add my original observation that Adams was the first president in American history to lose a re-election bid and retire peacefully to his home. And being first matters.