Unmissable.

This hard, I'm sure I'll forget something, off the top of my head and having a peak of what others have posted.

The Sopranos
Spiral
The Killing (The Danish version)
Borgen
Happy Valley
The Royle Family
Giri/Haji
Our Friends in The North (such a long time ago now, but a standout drama)
The Unforgotten
Stella
The Good Wife
Lots of Breaking Bad here, my son's favourite show ever! he tells me, I got told off for not sticking with it
Friends but not lately.
This Country

I knew I'd forget something Broadchurch (first series)

....and Madmen

Oh, yes, Terri, Madmen,
The Royle Family ( I rewatched The Queen of Sheba last night, laughed and cried, again, so well done. )
Dallas
The Fugitive
Dr Kildare
A Bouquet of Barbed Wire
The Politician's Wife...
I'm wandering down Memory lane now.🤣

Frasier
Big bang Theory
Young Sheldon
Mum
Morse
West wing
ER
Madam Secretary
Spiral
Only fools and Horses
Happy Valley

Funny how tastes vary, done of this eluded I couldn't watch once, tried but failed.
Those I do like
Vera
Morse
Ghosts,
This Country
Happy Valley (not that it was)
Original Midsummer Murders not last few years
Line of Duty not the last few though

My teenage granddaughter introduced me to Ghosts last week. The title had made me avoid it as I expected it to be scary and I’m a woos .

Not in the least scary but very funny. I love it 👻

Downton Abbey
The Crown
The Royle Family
Early Doors
Blue Lights

In addition to the above. I don't think it has been mentioned:

Six Feet Under

Also:

Outlander - though this is still on my watch list

And:

Better Call Saul - a spin off from Breaking Bad but better, IMO

Like Calendargirl - I love
Morse and Lewis .
Plus Endeavour .

All Agatha Christie inspired productions with Margaret Rutherford , Joan Hickson , Gwendolen McEwan and Julia McKenzie .
All David Suchet interpretations of Poirot and H . P portrayed by Albert Finney and Peter Ustinov .

All Sherlock Holmes from Basil Rathbone to Jeremy Brett .
Old Charlie Chan films .
Maigret the original and - why did they stop producing those starring Rowan Atkinson ?
Minder - I know a real life Arthur and Terry
The Professionals
The Avengers - I always wanted to be Diana Rigg
The Saint even if I thought that Roger Moore was a bit smarmy.
The Persuaders
Randall and Hopkirk - silly I know .
If Adam Adamant and The Man From Uncle were on - I'd watch them .
Silent Witness
Dr Who - right from the beginning .
All mainly nostalgia and escapism .....

I used to love watching the original Randall & Hopkirk. I’d forgotten about that one.

I would love to re-watch Blakes 7.

Also like to add

Babylon 5
Battlestar Galactica
Earth Final Conflict

I forgot about Blakes 7 .
I liked the evil Servalan !

The Thorn Birds, with Richard Chamberlain, was compelling when it was first shown.

Catastrophe ,Mum and Fleabag .

Hinterland
Hidden
The Bridge
Happy Valley

It’s strange - I watch lots and lots of TV, and yet the only ones I have watched of those mentioned are Miss Marple and Outnumbered.

I would add Keeping Up Appearances, The Vicar of Dibley and To the Manor Born. I’m sure there are others, but I can’t think of them at the moment.