Brief and to the point, Washington seems to be quite the opposite of New York City. Whether you like this or not depends on your individual urban preferences. If you prefer skyscrapers, noise, an infinite number of restaurants and shops, etc., then you ought to go for NYC. If a rather relaxed, green, clean, and historic city is what you are looking for, check out the capital.
A bunch of pictures basically tells the story. Except for the hideously hot and humid weather.
White House
1600 Pennsylvania Ave
White House backside
Capitol Hill
Green city of Washington with its tallest "building"
Washington Monument on closer examination
Federal Reserve Bank - Eccles Building
Federal Reserve Board
F.B.I. - Edgar Hoover Building
Lincoln Memorial
World Bank
Swiss Economist 