I think it'd be interesting to list all the good episodes of TNG and DS9 and stack them side by side. Every Trek show, unfortunately, has far too many rubbish episodes. In TNG's first two seasons, I can think of only one good episode: Q Who. Is there another? As for DS9, I think DS9 has the same proportion of rubbish, but because of its soap opera elements that dovetail between episodes, it's hard to notice one forgettable episode over another. I saw the episode Badda-Bing Badda-Bang last night, and it was really very stupid. As was Chrysalis, and Treachery, Faith, and the Great River.
I think it might be cool for people to just list episodes they really like of the Trek shows, if only in an effort to weed out the rubbish.
And the weird thing? TOS has many rubbish episodes, but they're so bad they're like an Ed Wood movie. Spock's Brain is so absurd, it kinda just has to be watched. Nothing in TNG, DS9 or the others gets that bad.