Doordarshan hosted a range of high-quality shows in its early days. Till early-90s Doordarshan was the only boradcaster in India. Till mid-90s it was not alone, but was still the most prominent one. Today a lot of other private broacasters have captured the mainstream television in India, but there are still a few of us who cherish those olden days of DD.
Its difficult to single out reasons for liking those old serials. However, simplicity, closeness to reality of the plots, mature direction, quality acting, diversity of subjects, and social relevance are somethings that characterized serials of those times. Just to remind you, a few of these truly excellent works of art are:
Malgudi days, Mirza Ghalib, Yeh jo hai zindagi, Trishna, Intezaar, Bharat ek khoj, Mujarim Hazir, Yugantaar, Katha saagar, Kab tak pukaroon, Hum log, Shrikaant, Byomkesh Bakshi, Karamchand, Neem ka ped, Apna Apna Aasmaan.
You can find a few people who cherish that time and those serials, on the Old Doordarshan Serials community on Orkut. You require a Google Account to access it. The community discusses these serials and other things about Doordarshan, such as old advertisements, public interest messages, news shows, etc.
And almost certainly, once in a few days, someone drags us into getting senti over our chidlhood days. :-)
Many things have come out of the discussions we have had on this community. A near-exhaustive list of serials is here. And a similar list of old-time commercials is here.
Also many people have written blogs about there memories of early Doordarshan days. A list with a few of them is here.