Season 1 was intriguing because the world was developed as were many of the characters. Season 2 dove into more character development and had a true antagonist who was ultimately defeated. Season 3 was a bit different, a bit unconventional, which I think threw some people off.
We did get more backstory development in S3. We didn't get a new antagonist however. Instead, the writers worked on Piper's arc, turning her from a traditional protagonist into more of an anti-hero. I really dug it.
OITNB is actually a rather complex show. Anytime you have twenty-five characters who are rather well-defined and who interact with each other in consistently intriguing ways, you know the writers are putting in some serious time and work.
My guess is that for S4, Piper morphs into the antagonist. Keeping a show with so many actors around for years has to be difficult as their salaries naturally rise. If they do keep it going, they'll probably focus on Piper as she turns into a hardcore criminal, and eventually as she gets out of prison where she'll either arc back to good, or face her eventual demise.
Either way, the quality of Orange is the New Black has been consistently high. It's going to have its seasons that resonate more strongly than others with the majority of viewers. But I hope in the long-run it doesn't focus on a broad base. It's a pretty unique show, and that's why I love it.