Fox has pretty successfully positioned FX as a place for more ambitious shows that wouldn't survive on a bigger network. To the point where I'm willing to give a show a try just because their track record has been good.
The Americans is the rare example of a very good show which never had a dip in quality throughout its run and absolutely stuck its landing.
I think one of the things that really made it for me was Keri Russell playing a character that was so different from a lot of what we were used to seeing her in.
"The Americans" is staggeringly good in my opinion.
I am blessed with a bad memory, so after a few years, I was able to watch the whole thing again, and except for a half-dozen things I remembered, it was like new content to me.
The only criticism is that you know the main characters are going to be OK, so it takes away a bit of the suspense. I wonder if you could have a similar show where the main characters are caught at some unpredictable point in the middle of a season, and then the show continues with new characters brought in to do the same job.