Washington's stations seem very repetitive. Downtown, once you've seen one, you've seen most of them. And in the suburbs many just look like train platforms. I don't see much remarkable about them, particularly given how recent they are - they wouldn't look out of place in Montreal (well, the first time ...). Am I missing something?
Yes. Washington's Metro completely changed subway design, moving away from the low, utilitarian tile-lined structures of the early systems and toward open, airy structures. It has been emulated around the world, from Montreal to Paris to the new subways of Asia. It also introduced many new technologies that we now take for granted on a subway system. It was also the first to combine the traditional roles of the commuter railway with an urban subway, and the first to emphasize on-train passenger comfort. Beyond that, it sparked a renaissance in mass transit in the United States.