The most unfortunate part of this episode is the character of Sheila. Not only does the actor give a pretty uninspiring performance, but the character is so poorly thought through and one dimensional. She's an unconvincing foil to Buffy. Buffy is such a teacher-pleaser in this episode that it's hard to believe she and Sheila can be lumped together for detention even by Snyder. Acting aside, we don't even see Sheila actually do anything bad, except get eaten.
And why was that character so thin? Because all the character development went into the first appearance of everyone's favourite evil couple, Spike and Drusilla. From the first moment you can just tell that these characters are going to be fun and I love knowing what they go on to become.
Without these two this would have been a very silly episode. Buffy trying to integrate her many lives (oil, and water, and a third unmeshable thing) through the mechanism of parent-teacher night was not a terribly interesting storyline. Not only does Spike liven up the scene, he break the rules by not waiting for the night of St Vigious, showing that he is badder than the bad guys. He's so convincing, so genuinely evil he can afford to show that he cares about Drusilla.
There are some clumsy logical errors -- Buffy has time to put her jacket on to save a vampire victim, but not grab a stake? Whoops! -- and Cordelia being crowbarred into the scene in the library to justify her screen credit would have let this episode down badly if not overshadowed by Spike. It is he who holds the episode together. He's such a dynamic character that even Angel pales next to him when they face off. It was inevitable that he and Drusilla would hang around a while to cause more damage.
Verdict: "It's time we had a little less ritual around here, and a little more fun!"
Hmmm ... I think my favourite bit in this episode is the frigging Annointed One getting his comeuppance - it's so quick and painfree that it almost seems anticlimatic. Almost ... but I hated him, so .. yay!!! I like that Spike whisks in and so effortlessly deals with the remainder of last season's Big Bad. But I must admit that the rest of this episode is a bit meh for me. I mean... I think Spike and Drusilla ride in with such promise about how evil and unremorseful they are going to be, and I guess they are in a way, but knowing where both their character arcs go, I dunno, I felt that this beginning somehow was never really followed through with, in the end. The other thing about Buffy is - it's always the Devil you know that wreaks the most havoc.