My idea of a soap is the writing is simplistic and the acting is overly emotional. I will agree that the writing in Downtown Abbey has become more simplistic, but I think the acting (except for the Americans, Elizabeth McGovern, Shirley MacLaine) is still believable. (On Selfridge, I'm still amazed at how well Frances O'Connor pulls off an American accent. She sounds so natural).
EastEnders is the only soap I watch, so I'll use examples from that. In this show, they start storylines that have no resolution. And they count on their audience just forgetting or overlooking key plot points.
EastEnders takes place in the London community of Walford. There are more deaths in Walford than in anywhere else in the world. That's because a rule in soap opera is that when an actor wants to leave the show, they kill them off. And EastEnders took it to the extreme when they brought back a popular character (Den Watts) that was killed several years ago. I was a bit surprised when Julian Fellows killed off Matthew Crawley as it borders too much on soap opera. And yet he allowed O'Brien to just escape out into the world.
The acting on EastEnders is so unnatural. Everything is played at the highest emotional level possible. Plus each episode ends on a cliffhanger, so you have to tune in to the next episode.
But yet I and thousands of other people (including Brad Pitt and Angelina Jolie) tune in to two episodes per week of EastEnders.
With Mad Men (and others dramas) the acting is very natural. You can believe that these are actual people in interesting situations. The actress who plays Sally is so perfect. She's always believable and doesn't slip into the drama queen teens on EastEnders.
Yes with Mad Men there's a lot of bed hopping which you find in soap operas, but it seems more character driven rather than in soap operas where the bed scenes just seem to be written to fill out the episode.
That's a lot to simply say that I think the difference between drama and soap opera is that in drama, the characters seem to have purpose and have an arc and the emotions are played in context. In soap opera, the character arcs are all over the place and are more caricatures. And the emotions are played like Acting 101.
If anyone ever tells you that you put too much Parmesan cheese on your pasta, stop talking to them. You don't need that kind of negativity in your life.