Everyone is bagging "Crossfire". What's wrong with you people?! Haven't you ever been infatuated with someone inaccessible at work?
I'm also surprised to see "Sword of Kahless" chosen frequently. Sure,the plot isn't very original, and there's isn't exactly much food for thought, but I always enjoy it.
No-one has mentioned "Accession" which I don't find very interesting. And even though "Broken Link" set up some great episodes (like "Apocalypse Rising", "The Ascent" and "The Begotten") IMHO it's not spectacular in itself.
I also don't particularly enjoy "Indiscretion" ; "Return to Grace" on the other hand is great!
But this is one of the best seasons of trek. "Muse" is the only unwatchable one episode, as is any featuring Lwaxana. Only Ezri, Keiko and Zek approach her in terms of annoyingness.