Finished S4.
As someone who thought S2 was the best, S4 goes along with it. Piper's arc is actually interesting though she's a complete idiot for about half of it. Let's just say I haven't cared about her since S1 and S4 made her a tolerable character again by making her reap what she has sown.
Of course, what makes OitNB is the cast outside of Piper. Their stories in S4 are either continuations from what we know from previous seasons or brand new backstories. S4 comes across as the climax of a lot threads we've gotten so far, but I'll keep hushed about that.
OitNB has always been socially aware, but nowhere to the degree like it is in S4. The prison being run by a for-profit company snowballs into what I felt was the most rational and terrifying result, considering these prisoners are women of different races, ethnicities, and backgrounds.
By the end, I will say I was tearing up a few times. You can argue that some things are hamfisted and sort of predictable, but the story does coalesce the theme of how pure goodness can and will be destroyed by institutional infrastructures. This hits home by the depictions of what these women have to go through.