When Orange Is the New Black first aired on Netflix in 2013, it was like the TV gods had grinned down upon us. Here was a clever, thrilling comedy drama that was also full of characters we don't usually see in big shows. The women were all shapes and sizes and races and sexualities – and it felt like an irreverent but genuine warts-and-all insight into prison life for females in America.

But above all, there was serious jeopardy. White, pretty, privileged Piper was wrenched from her lovely aspirational life and hurled into a prison cell for something she'd done when much younger and stupider – and it never occurred to her that she would be one of those people. 

We saw, with horror and fascination, the prison system through her naive eyes as we waited fearfully to discover whether she would get out or not, becoming totally invested in the narratives of her black, Latina, elderly and transgender prison-mates along the way. There was feminism, powerful statements and lots of humour – but most crucially there was an I Can't Stop Thinking About This Show level of drama. 

And that's why it should have ended after one series. It would have remained a perfectly formed and impactful piece of TV – but now, as series four airs on Netflix, it's become diluted by repetitive storylines which are hard to truly care about. 

Four seasons in and the show feels flat and a little dull. There's no meaty plot to keep the momentum going, nothing to fear and nobody to really invest in. The jeopardy of prison life is gone, and now the show has become a little farcical – take Alex chopping up a hitman's dead body in the first episode of series four, or Piper becoming the jail kingpin as the new inmates arrive. It's just all so difficult to believe in, or care about. Litchfield is less like a prison, more like a playground where the characters are play fighting, resigned to the fact they're not getting out. 

In a way it's impressive that the show keeps going – but I'm worried it's not heading anywhere exciting. We've had all the best possible storylines about daily prison life, the characters' flashbacks to their pre-jail lives, romance, sex, loss, politics and violence. So now it feels like storylines are being repeated or dragged into desperate realms. Even the fact that series four is about the prison becoming overcrowded with new inmates is a little weak. There's no sense of danger left within Litchfield so they're chucking tons of new characters into the mix to try to create tension. 

OITNB was once up there with the best TV I've ever seen – but it's one prison show that deserved a shorter term.

Orange is the New Black season four is available on Netflix from Friday 17th June 2016