I watched from the beginning. It was on YouTube, maybe still is. The episodes are short, but after a while I lost interest - it is very simply made on small sets and it seemed to endlessly circle around things but never get to the point.
The show was very popular at the time though in the US - it was not ever released outside the US, or at least not widely, so it remained unknown mostly in Europe until the Tim Burton film.
What I understand about it (but American users of the board will probably know this better) is that it became only truly popular once Barnabas entered, who is not in it from the beginning - so it may be a case of just sticking with it. I don't think all episodes are on YouTube though, although YouTube content is constantly changing of course.
The revival I liked a lot though.
I used to have a few episodes on tape, and a couple of compilations of different scenes. I watched a few full episodes through Hulu when you could still watch videdo through their website on a free account. But your account of what made Dark Shadows popular sounds right with what's been said about the show. I personally found Barnabas more likeable at first on the revival than the original. He seemed more evil in the original series at first.