Many of the "classics" are better remembered than re-watched.
True classics can be re-watched, and there are very few. The common denominator of the true classic, beside a great script, is a genius of a central performance, by a comic craftsman.
- Ronnie Barker in Porridge/Open all Hours
- Leonard Rossiter in Rising Damp
- John Cleese in Fawlty Towers
- Arthur Lowe in Dad's Army
- Dermot Morgan in Father Ted
- David "I learned it all from Ronnie Barker" Jason in Only Fools and Horses
There are others of course but Ronnie Barker is the stand-out comedy actor for me. His characters were nothing, zero, nada, like the actor himself. It was proper acting rather than reading funny lines in your own voice.
As for forgotten ones, I used to like "Sorry" with Ronnie Corbett