In which ways was Buffy the series ground-breaking in terms of the mythology of vampires?
Well, the first thing that pops into my mind is that in Buffy, vampires are not exactly all-mysterious-and-beautifully-scary. I remember in the episode Lie to Me, when Chanterelle says that vampire are innocent misunderstood creatures of the night, well it's the common conception of vampire, the first image people have when you say vampire (unless the first image they have in my mind is blood and stakes). In Buffy, vampires are more human than mysterious. They can be cowards, they can be scared (like in Into the Woods, when Spike takes Buffy to a lair and the vampires are like "Slayer!...*run away*". That's the kind of things you don't see in every vampire movie).
They can have feelings and can be threatened by humans. They can be viciously intelligent or kind of stupid and just guided by the desire of blood. The whole poetic aura of vampires is broken in Buffy, which is, now that I think about it, an unique perspective and kind of brilliant! Vampires in Buffy are different from Lestat or Dracula, they are much more human, with much more nuances of personnality.
Or females and power?
Well, before Buffy, there was already Xena so it isn't really ground-breaking, even if quite unusual. The difference is, Xena was kind of new in the mythologic (in series or movies) area while Buffy is more new in the horror-area.
