"Hush" is widely regarded as one of the best upisodes of Buffy. Joss Whedon pulls all the stops out to deliver an episode with a nifty gimmick (over 60% of the episode is without any dialog), truly spooky villans, action, romance and great heaps of plot & character development.
Joss says in his commentary that the central theme of the epsiode is "when we stop taking, we start communicating", and in the teaser and first act we get the communication failures - the not-yet-couple who start babbling wenever they look like they're getting anywhere, the guy who can't express his feelings with words, the wicca group who are all (misused) words and no action. Plus there's the psych lecturer on how putting your thoughts into words you lose something (just like LJ postings ;-)
At the end of the first act, we meet the villains, described in the script thusly: "He's old, bone white, bald -- Nosferatu meets Hellraiser by way of the Joker. Actually, he looks kind of like Mr. Burns, except he can't stop his rictus-grin, and his teeth are gleaming metal.". Straight out of the Grimm fairy tales, these guys are in many ways scarier than your average big monster with fangs'n'claws. The way the glide about, and their politeness is downright disturbing. Anyway, for their own nefarious ends they steal all the voices of Sunnydale, leaving us without spoken dialog (bar machines) for most of the rest of the show.
Our characters find that they are still able to communicate - expressions, gestures, mime - albeit with some writing (including the fantastic Exposition-via-OHP sequence). Our couple finally manage not to talk themselves out of a first kiss, the guy manages to proves his feelings with actions that speak louder than words, and the two wiccas who were actually interested in magic get together. Oh, and they still manage to beat the bad guys, plus there are some nice touches on how the rest of the population copes (the bank is closed, but the liquor store is doing a roaring trade).
In terms of the ongoing arc, two relationships are cemented, and the introduction of a new recurring character sows the seeds for a third, truly great, one, plus there ave various other bits of plot & character development. The episode's ending is, perhaps, inevitable: "We need to talk", they agree, but now that they have their voices back they're unable to speak.
Contrast with: Joss exploring the exact opposite direction in the episode which finally knocked "Hush" off the top spot - the characters communicate their deepest feelings (whether they want to or not) through the medium of song in "Once More, With Feeling!".
