I love Deep Space Nine a whole bunch... but if we're going to be honest it wasn't as successful as TNG because for most people it wasn't as good as TNG. And there's nothing wrong with that, different strokes for different folks as they say...
Andymator, you keep reiterating this argument that everybody thinks 'People didn't like DS9 because it was too deep, too complex, too above their heads!' In this entire thread maybe one person has actually said that.
The rest of us are saying, scope of appeal and size of appeal are two different elements. A lot more people watched Survivor than The Sopranos, but the people who watched The Sopranos got a whole lot more on average out of it. In this case, a lot more people watched TNG, but the DS9 viewers got the same amount on average as the TNG viewers. Is quality of a show a measure of width or height? I say height. And if you say width, be prepared to defend Justin Bieber.
Nobody is saying that every TNG character had complete amnesia between episodes. There were arcs, there was character development over time. Most of that development was limited to the main cast, and the only exceptions are really O'Brien and Ro. DS9 had development for most of its huge secondary cast.
And, nobody is saying DS9 had absolute linkage between every single episode whereas TNG had a total reset every week. It did, however, base a great deal of its standalone episodes on previously established storylines, and the amount of background information you needed to get solid footing in the story was far higher, even for most of the standalones. Look at a standalone episode like The Ship. How can you possibly understand why the Gem Hadar and the Vorta act the way they knowing the things established in To The Death? Without that information, the resolution would not make any sense, and it's the same with Rocks and Shoals. And then there's Rapture, it's a standalone episode but none of it makes any sense if you don't know the entire history of Sisko being the Emissary. TNG had arcs like Sins of the Father/Reunion/Redemption, but in general, any episode can be watched with a completely blank slate and gotten completely.
Rocks and Shoals is not deeper, more complex, or better television than Cause and Effect. But you do need a lot more previously established information to know what's going on. And that's all people are really arguing.