How does Artyom's continuing progress through the Metro let him accrue knowledge and self-confidence, and a growing access to spatial freedom? How does his discovery of the photo of "little Artyom" mesh (or not) with this process?
What does Moscow now look like, above-ground?
What do you think happened to the Librarians? (Pause to Google images of the Lenin Library in Moscow: it's quite as grand as the subway stations!)
Any further thoughts about trading (a kind of proto-capitalism), racism, and religion, as they're manifested in the Metro?
What kinds of roles do children play in the novel? How do the children who appear serve to illuminate Artyom's past (childhood) and future life (potential fatherhood)?
Trying to avoid a spoiler: how is the revelation of the novel's last couple of pages prepared in earlier chapters? Should the reader find it persuasive (increasing the impact of Artyom's final mission) or distrust it on the basis of earlier examples of psychic connection such as what we saw under the Kremlin?
Once you have finished the novel: how might the Dark Ones fulfill the prophecy (about The Book) that Daniel passed on to Artyom?
It seems likely that the novel draws more on popular culture in general than on the particular works of science fiction that we have been reading, BUT: how would you compare the mutants Artyom encounters to the aliens we've read about, or Čapek's newts? How is the voracious liquid or whatever it is they run into under the Kremlin (explained as originating in a form of biological warfare) like or unlike the ocean of Solaris?
What is the role of dream and daydream in the novel? Is it plausible that Artyom is a Chosen One, given his experiences up to this point?
What does the end of the novel mean for the remnants of civilization living in the metro, and does the (sudden?) difference between Artyom and his companions suggest anything about present-day discourses of militarism or macho-style masculinity?
How does Artyom himself align with the various forces, ideologies or guilds he encounters in the metro?
Again, what are the associations of the underground? The place where dead are buried (thus: Hades or the pre-Christian Rusian преисподня), the place where water flows before emerging into a well or a river (thus: locus of invisible filters and sources); a spatial equivalent of the unconscious or subconscious (thus: source of drives and desires that perhaps can't be allowed to emerge onto the surface)?