I wouldn’t go quite that far, but certainly don’t think it’s a particularly good litmus test for the series.
But I also don’t really like the Pack or the one with the ventriloquist dummy (sorry, I forget the title), which other people tell me are brilliant eps, so whadda I know.
“The Puppet Show.”
I agree. Never got the love for that episode. But “The Pack” gets props for a quote if nothing else:
*Giles: Xander’s taken to teasing the less fortunate?
Buffy: Uh-huh.
**Giles: **And, uh, there’s a noticeable change in both clothing and demeanor?
Buffy: Yes.
Giles: And, well, otherwise, all his spare time’s spent lounging about with imbeciles?
Buffy: It’s bad, isn’t it?
Giles: It’s devastating. He’s turned into a sixteen-year-old boy. Of course, you’ll have to kill him.*
*Xander: On behalf of my gender, let me just say, Hey!
Giles: Yes, let us not jump to conclusions.
Buffy: I didn’t jump. I took a tiny step, and there conclusions were.*
(Yes, its from a different episode, but it fits.)
Agreed that it isn’t a good litmus test for the show, but it’s one of my favorite episodes of the entire Whedonverse.