I think Buffy holds a unique place in my heart because:
1) I've never seen a show before or since that in which I've loved so many of the characters. Most shows I like 2 maybe 3 of the cast and put up with the rest because they just tend to bore me. Not with Buffy/Angel- I like almost all the characters and love their interactions.
2) I like the structure, the narrative arcs of the seasons, the character growth that most of the seasons exhibit, the Big Bads- bad guys that have shades/dimensions to them. If another show has any of these elelments I like them all the more.
3) I love kick-ass heroines. They were much rarer before Buffy, at least on television, and I think Buffy, Willow, Faith, Cordy and co were trailblazers in this regard. Punching/zapping/stabbing people and looking cool doing it.
4) I love the humour, the wit, the symbolism and the metaphor. It's basically a very clever show on a lot of levels.
5) The shows are about growing up, dealing with life, finding meaning and purpose in a harsh, unforgiving world that seems to lack a comforting religious/moral framework. If you're strong, if you rely on your friends/family, if you recognise and try and conquer your flaws then you'll have a life worth living even if, in the end, you don't make it.
6) As a Brit I appreciate that Joss is an anglophile and that many of the characters I like are fellow countrymen. Sure there a few cliche's thrown in there but the writers always go beyond the obvious to flesh out the characters. Giles, Wesley, Rayne, even Spike have lots of great moments.
I love these boards with so many different, nice, lovely people on them.
I like the comics because they seem to be keeping the 'verse alive where other fiction has fallen by the way side.
I love a lot of the fan fic that's written about these characters- some of it is good and heartfelt and really imaginative and some of it is lazy, derivitive and unintentionally hilarious. Still love to read it though.