This airport is a national treasure. It's a vintag...

This airport is a national treasure. It's a vintage facility and looks the part--much more appealing that the concrete monstrosity that is Dulles. You can just imagine passengers boarding shiny aluminum DC-3s on the tarmac back in the day. It's uncomfortably close to DC, so close that planes landing from the north have to follow the snaking path of the Potomac to avoid the prohibited airspace over The Mall on the River Visual approach.
Lots of comments in other reviews about the people who work here. It's not fair to blame the airport for the airline employees. If you don't like crappy customer service, don't fly the cut-rate airlines. As for the TSA employees... I fly all the time, and they're the same from coast to coast. At least they're not collecting unemployment, which is basically their only other option in life. I know. I'm mean. But you know it's true. Once upon a time, in the 20th century, gate greeters were employed by the airport, and cared about their jobs. Now we have the TSA. Deal with it or write your congressman.
Parking at the airport is expensive, but here's a local trick: you can park at the Van Dorn Metro station (three stops from DCA on the blue line), then arrive at the airport after a quick light rail ride. The kicker is: though there is a "long term" section in the Van Dorn garage, the station has no provisions to charge for more than a single day fare. Yes, you pay for one day when you leave. You feel guilty, but it's the setup. Spaces are limited, so have a backup plan.
If you find yourself blessed with an extended layover, walk out to the Metro station, buy a Smartrip card, put a couple bucks on it and ride the yellow line 4 stops to L' Enfant Plaza (named after the designer/civil engineer of DC) to hang out on The Mall. If you're really adventurous, use the same Smartrip card (or singles) to ride the DC Circulator bus to the Jefferson and Lincoln Memorials. If you hold on for one more stop, and get off at Archives, you might be able to duck in to see the Declaration in just a few minutes if it's the off-season. If it's food you seek, go a little further to Gallery Place (Chinatown). Or just walk to the Old Ebbitt Grill, a classic DC bar.