Regarding some of the mentioned lower tier episodes people have mentioned, I have a good and bad view on them.
"INVASIVE PROCEDURES" - Good: I can understand why Verad is never counted going forward. He was joined only for a few hours, certainly not long enough for a real blending to occur. Whatever memories Dax might have gotten at the end of that episode might easily have been forgotten in a day or two. However, I do feel that the back and forth joining of Dax to Jadzia is what triggered the breakdown of the barrier keeping out Joran... doubt it's a coincidence that barely a year later is when that happened when the barriers were working for 80 plus years. And Tim Russ does a good Klingon. Casting John Glover was genius. Bad: like "DAX" in season 1, another Jadzia episode that barely actually involves her.
"MELORA" - Good: Klingon restaurant owner was a treat, and his first appearance. A shame we didn't see him more often. I always thought after Martok was given a permanent detachment on the station we might get to see him more. Bad: Melora really comes off as unlikeable for too much of the episode.
"RULES OF ACQUISITION" - Good: Putting the most important piece on the DS9 chessboard in a Ferengi episode? GENIUS! Never saw that coming. Bad: honestly, I never found this one bad.
"SECOND SIGHT" - Good: Great new views of the Nebula class ship. Reigniting a dead star was a great concept, and Seyetik was very entertaining. Bad: I'm sorry to say this episode was pretty boring.
"SANCTUARY" - Good: One of the ONLY times the franchise actually dealt with not being able to communicate. Loved that, and it would happen more often if not for television. Bad: the Skreeans looked like brats. They were offered an entire planet, but they were hung up on Bajor being Kentanna? And she made Kira feel guilty for backing a decision that actually made sense for her own people? That's some nerve.
"PARADISE" - Good: Everything about this one was good... Bad: Until the ending. It really soured the message that NO ONE wanted to leave.
"PLAYING GOD" - Good: A day in the life of Jadzia. And the voles were cute in an ugly way. Good scifi concept with the protouniverse. Bad: Arjin was badly cast. One of the only times DS9 dropped the ball there.
"PROFIT AND LOSS" - Good: Armin Shimerman acted the hell out of this one, as usual. And having Garak appear automatically elevates any episode. Bad: CASABLANCA on DS9 just didn't feel right.
"THE COLLABORATOR" - Good: Nana Visitor, as usual, doing an excellent job. Bareil comes off as very honorable here. And Winn being Winn. Plus, Rene's acting choice in his office when he and Kira were talking definitely planted the seeds for the writers later on. Bad: There are points where I can feel the episode just drags.
I'm going to add my own episode...
"RIVALS" - Good: Bashir and O'Brien is always gold. Quark being Quark, as usual, is a joy to watch. Bad: The episode just didn't feel like it belonged on DS9, other than what I mentioned before.