For the most part, I think TNG's middle seasons were some of the best eps in the entire franchise (second half of two through about the end of five). After that, my head starts to hurt from the liberal use of treknobabble and "magic-particle of the month" solutions to everything. Some of my favorite episodes were most straight forward and didn't get too fancy with the premise. Like Contagion (computer viruses, teleportation, other goodness) and the concept of the Picard Manuever was IMO the most ingenious and most often ignored piece of trek ever produced.
Then you turn around and hear Geordi say something like "If we modify the deflector grid to emit a fancynamium pulse, we might be able to seal that quantum hyperbole that's been causing all the Klingons to turn blue." I can sort of see this for a science mission, but it gets a little absurd in combat situations where the preferred tactic of EVERY starship commander (from the Defiant to Voyager and everything in between) is for the Chief Engineer to modify some piece of equipment to emit a high frequency problemsolvedium beam?
Nobody EVER repeated the Picard Manuever... not even Picard! And that was one of the craftiest things I'd ever seen on Star Trek.
I like DS9 on its own merits because it's well written, but it has some flaws TNG escpaed. I absolutely loathe Voyager, and I kick people who express even the slightest praise for it.