From the first 3 minutes of season 4 we know something has gone terribly wrong for our characters and the world they live in. It had been building over the last three seasons underneath the glitz and glamour you could FEEL an animalistic hatred stirring...
This episode makes it clear that the golden days have ended, and it's done in such a brilliant manner.
Suddenly, we see muted colors, we notice the sheer amount of disparity, even the weather is unsettled. The weight of what is about to happen is written into the very flesh of the characters faces. It is so unsettling because we as the audience know what is coming. The characters however, can only feel the growing tension, as the world slowly dissolves into a living nightmare around them.
This show has proven over 3 seasons that it is an absolute masterwork of historical fiction, and the 4 season makes it clear that the bar will be raised yet again.