Once upon a time there was this evil hellgod who was banished from her kingdom and imprisoned within a human boy, in the human realm. This angered the evil hellgod, although she made the most of it by wearing really sexy dresses and high heels. Also, she sucked out people's brains for fun. Far and wide, she searched for the key back to her world that would open the portal between dimensions.
But there were those on earth who opposed the hellgod, and fought to keep her from creating a rift between the realms. Sadly for the earthly realm, her foes consisted of weak, foolish monks and dumb knights with magic horses. Quite naturally, they realized they were no match for her, depsite hundreds of years of preparation. The knights and the hellgod searched for the key: the knights hoped to destroy it, the hellgod hoped to use it. Unfortunately for both the knights and the hellgod, it was the dumb weak monks who had actual possession of the key. Unwilling to destroy it, they instead transformed it into a little sister for Buffy, to teach her a lesson about sharing. I mean, so she would protect it.
Unfortunately for said key, this turned a very small object that was easy to hide into a large teenage girl, and placed her in the same town as the hellgod. Ultimately, the hellgod tracked down the key and used her to open the door, letting in lots of flying dragons. Buffy, tired of all this newfound "sharing", jumped off a tower to make it stop.
My favorite post on that site is their elaborate, play-by-play evisceration of the worst "Buffy" episode ever, "Wrecked." This is the one that used Willow's "magic addiction" as a barely-metaphorical metaphor for a hideously preachy and awful don't-do-drugs lecture. Boils and Blinding Torment's recap takes the whole thing apart and exposes every preachy moment, every plot hole, every heavy-handed moral. My favorite line from the recap: "Willow, you summoned me with your floaty stoner magic."
Other great articles from the site: "The Idiot's Guide to Continuity" and "The Post-Season 7 FAQ."