Not sure, as I've never been hip.
I think a lot of things were changing in the mid-60s through early 70s. Dark Shadows did reflect those changes.
A lot of the established soap operas started out as radio programs and their story lines were well established after 20-30 years.
DS was completely new, related to a younger audience and had a unique story line.
It grabbed attention like The Beatles, Vietnam, folk music, mini skirts, body paint, exaggerated makeup, etc. And television had become the entertainment mecca for kids. It was perfect timing.
It was a bit rebellious/scandalous to what Mom and Dad were watching and kids flocked to it.
It has stood the test of time because those kids that watched have kept it alive in their memories, as part of their youth. Just like The Beatles and everything else in that time frame.
My mother still listens to music from her youth, I listen to the music of my youth (Bobby Sherman
), my nieces and nephews do the same thing.
Let's face it, none of want to grow old, so we cling to our youth. And in DS, no one ever grew old, no matter how many centuries they traveled. I hate them all!