Now, what's this business about sparkley vampires?
This may be a little opinionated, since I am an avid Buffy Fan and Anti-Twilight, but here goes:
1. First and foremost, the vampires. In myths and legends, Vampire are, in one word, evil. They are bloodsucking creatures of the night with an aversion to sunlight and a fear of things holy. They can be killed Von decapitation, fire, and a stake to the heart.
Buffyverse Vampire embrace these myths, taking on a human appearence and shifting into "game-face" (yellow eyes, bumps, and fangs) at will. Sure, some Vampire may have quirks and essentially good personalities, but they all have the same features...