I'm actually not familiar with most of the music in the playlists, so I'll definitely have to listen to some of it. However, seeing explanations of the songs I did know were particularly helpful.
For example, the explanation for Linkin Park's "Papercut" in New Moon. I always thought it was a kind of silly choice, since the meaning doesn't have much to do with the scene... I always just assumed that she picked it because of the title. However, when I read the quote and considered the general sound of the song with that scene, I could see where it fit, in a weird way. It wasn't about its lyrical accuracy. : )
Another one was KoRn's "Twisted Transistor" in Book 2 of Breaking Dawn. I never understood what that was doing there, but seeing that it was about Leah made it make a lot more sense to me.