I forgot "Going Through The Motions"
That's a song anyone can relate to. Which is the bueaty of a lot of the songs on "Once More With Feeling", the themes of them are general enough to be relatable and character specific enough to drive the plot forward.
When I was first getting into the show the first great combination of episodes I saw was "The Becoming 1 and 2". Emotional rollercoaster throughout the whole thing. You couldn't not feel for Buffy when she stabbed Angel. Angel and Spike seemed like such bad villains then, but Angel as a good guy turns things completely around. And Spike...well, I can type up something cool on him whenever we get to favorite characters
I tend to like the unusual episodes the best, the ones that divert from the usual plots and tendencies of the show. "Superstar" and "Same Time, Same Place" are good examples of that.