I grew up watching YM and YPM, and enjoyed them from the start. It's what made me interested in politics and government, and really I learned a huge amount from both series, while having a laugh too. If the original series and cast had been replaced with this reincarnation, I doubt I'd be who I am today.
The writing isn't as sharp, and it's that which makes this mediocre. Simply trying to pluck catchphrases, themes and current affairs from the modern era and stick them in place of their 1970's equivalent isn't enough. Nor is using coarser language, which just isn't needed. What the writers needed to do was stay true to YPM as it was originally, and take forward the characters. Then use hypothetical, but realistic scenarios. Doing that, the script would almost have written itself.
What many people remember about YPM/YM is that so many of the things that were depicted happened later in real life. Obviously not completely, but rewatch the episodes, you'll see what I mean. Not so here. Fantastical isn't too strong a word. Then there's the way the characters behave. Again, stupidly sums it up. The original series may often have been farcical, but it was within context, and the character were nuanced and realistic. Not so here.
It is true, the stage play has been taken and transferred to the screen, and while that could work, it doesn't here. I can't imagine watching the play and enjoying it any better than this series. What should have been done is that the writers and producers left Hacker, Humphrey et al in the 1980s and gave us new characters. That may have worked. This feels cobbled together and just plain wrong.
So, why three stars? It isn't rubbish, it just isn't good. I'd have loved to give it 2.5 stars, because that's what it deserves. The effort is there, the actors couldn't do more to make it work, and it is nicely produced. But the writing, directing and overall concept mean it's mostly wasted.