One of the best jobs I ever had was as a props buyer for Prime Suspect II. Every day I was handed a wad of cash and a shopping list and let loose on Manchester, buying anything from a garden shed to sado-masachistic hardware - a whip from the Corn-Exchange; handcuffs from the Arndale Centre Market; a dragon mask from Affleck's Palace ..... I had to kit out the murderer's caravan/torture room.
Got some really funny looks as I shopped around. "Do you have any whips or canes? No? Oh. How about handcuffs? Any heavy chains? How about a cattle prod?"
I must say, though, that I've found the plot line weak at the end of two episodes that I can think of - in P.S. II where the baddie is surrounded on the beach and he runs ...... into the sea!

Duh! Where did he think he was going? France? Ireland?

Risable.
And I thought the scene of the young girl with Tennyson's sister at T's late father's house and her subsequent arrest, in P.S. VII, was very poorly handled. I suspect they were over-running terribly so cut it to ribbons. All the info we needed was there, shown in a series of brief scenes, but it ran against the grain of the rest of the show stylistically.
Nevertheless, the series has, on the whole, been a triumph both for the cast and the crew, many of whom had worked on previous Granada triumphs like Sam, Family at War, The Jewel in the Crown, Brideshead Revistited, to name but a few.
We tend to think first of the BBC when reflecting on the excellence of British TV, but the output of Granada TV, when it was an independant company, should not be forgotten.