I've been watching re-runs of Coronation Street from 1986 on ITV3 for the last week or so, episodes which I probably watched when they were originally broadcast.
The first thing to say about them is that the show was far funnier then, with many more comic characters and storylines than there seems to be now (I gave up watching it regularly a few years back, partly for that reason) rather than the Eastenders-style grimness which seems to have crept in since, with lots of sparkling repartee between brassy Rovers Return landlady Bet Lynch and the conniving showbusiness agent (and her future husband) Alec Gilroy, the newsagent's shop-running duo of Rita and Mavis (and her hapless fiance Derek) and the malapropisms and wall-adorning "muriel" of pub cleaner Hilda Ogden. The main difference there is the number of boxed keg beer taps on the bar - something you don't see much now outside of Sam Smith's pubs - rather than the more traditional handpumps which have since replaced them.
The main reason for the drop in quality is no doubt the increase of episodes from two to six a week, requiring the scriptwriters to stretch out storylines and make them more melodramatic.
That problem funnily enough is one which the only soap I now watch regularly, the Australian Neighbours, seems to have overcome, despite being broadcast daily, mostly maintaining quality and the fine balance between comedy and drama.