DC's system is OK. It suffers from being both a commuter rail system and a city transit system mashed together. It needs more tracks so that maintenance can be performed without massive delays and so express trains can be run. Coverage is lacking. It's good if you're going places it serves, but there are a lot of places it doesn't go, like Georgetown. And the hub-and-spoke model makes it quite painful for a relatively decentralized city. Going between, say, Bethesda and Tysons is physically possible but takes ages because you have to go all the way downtown first.

It gets a lot of things right and is great if it has a good route for the trips you want to make when you want to make it, but mostly it shines because the situation is so much worse in any other American city that's not New York and maybe Chicago.