Matt only appears twice in the book, and never evolves beyond his obsession with distributing his toxic newsletter. Tom Perrotta said that he initially envisioned Matt as a bigger part of the book. On the show, Matt evolves into a much more compassionate, nuanced character over the course of the season.
This episode essentially wraps up the TV show's adaptation of the book. While the episode's final scene is a fairly faithful adaptation of the book's ending, the various characters' story-lines leading up to that moment are different.
As the GR are contemplating carrying on with their grand plan to make the townspeople "remember", amid the worry of the disappearance of their leader and Jill's willful induction into the group, an orchestral version of Metallica's "Nothing Else Matters" plays almost in its entirety, with no words spoken during the long scene.
After one of Kevin's sleepwalking bouts, he is sitting in a diner with his father and loud instrumental steel guitar music is playing in the background. This music is an existent pop song, a 1959 number one hit by Santo and Johnny Farina titled "Sleep Walk."
Damon Lindelof admitted that he wept like crazy after reading the final scene in the novel. It was always his intent to end the season with this scene, albeit with the added bonus that the series had just been renewed.