I love travelling on the Washington Metro (OK there are times - in the rushhour when I've waited for a seemingly unending time in L'Enfant Plaza making the connection between the train from Capitol South on the Blue Line to the yellow line to Huntington, when loads of green trains come through & the platform is full - and when my train finally arrives there are no seats - that I have less than generous thoughts). Mainly it's good fun. On my early visits to the City I would ride the Metro discovering new areas on the weekends when Congress was closed. (I fell in love with Rockville as a result of riding the Red Line.
There is a very useful website - http://www.wmata.com/ which has details of the system and the various stations. As I write at my side is the very informative "StationMasters DC Area Metrorail Atlas".
GoRemy has written and performed a great song about the Metro - a little critical - but tongue in cheek, and I enjoy watching it out of affection for the Metro.