Still have yet to finish The Americans, but the five seasons I watched were utterly immaculate. Boardwalk hits higher heights and its first four seasons are excellent and have some of my favorite TV performances in the last fifteen years, but the final season really poleaxes the whole deal. It isn't unwatchable by any means, but you know they had three seasons' worth of content they had set up and had only eight hours to rush through it.
I know. I got to the David Copperfield episode, thought it was a fantastic way to end the series with that sense of uncertain cynicism . . . and then I watched one episode afterward, almost a year later, and my favorite character died in the lamest way and I just never got back into it.