This was the first Buffy episode to make me cry, and it turns out, it still does. Not Jenny's death per se, but Buffy and Willow's response. So heartbreaking. The other standout sequence is the chase between Angelus and Jenny. The camera angles, editing and low lighting all create a superbly creepy and scary run through the school culminating in the horrible neck snap.
The scene in Giles apartment, where he thinks Jenny is waiting for him upstairs (and I suppose she is) is brilliantly portrayed by Giles, almost to the point where you think there has been some mistake and Jenny really is waiting for him. *sob*
"You know, I think there may be a valuable lesson for you gals here about inviting strange men into your bedrooms."
I think this episode raises the stakes for the audience. It's here, at the climax of this episode, we learn that all the rules don't apply in Jossverse and that all bets are off - anyone can die, even a main player. And so too, Angelus kills Jenny in an almost anticlimatic, off-hand way, such that I think it becomes all the more shocking and heartbreaking. He doesn't break a sweat. He doesn't stalk and play with her (much). He just does it. Dramatically and with a gorgeous backdrop of the night, framed in that window. And he glorifies in it too but more so because of the anticipated effect on Buffy than for the kill itself.
This episode is about passion and the bookend narration is by Angelus. I think this works beautifully to use the change in POV to show that we, the viewers, should expect the unexpected. That this is not all going to go the way we want it to go. Evil, Angelus may be, but as Willow points out, he is still obsessed with Buffy. Sort of the dark to the lightness that went before.
Even having watched this episode many times before, I still cried in that moment that Giles calls Buffy to tell her what has happened. And it works well. Despite watching it from afar, removed, with Angelus looking through the window, it's still very powerful and desperately sad. And there is a really great shot of Buffy as she sinks down to the ground, absorbing the enormity of what has happened and you can see the realisation dawn to her that this is *real*.
I want to finish by saying how rightly it depicts how CREEPY it is for one's Vampire to sit and watch one sleep. (*cough* Bella Swan *cough*)