I don't know that I loved this series after it wrapped up. Many of the plot points seemed to go underdeveloped, and none of the characters were interesting enough / the situations they found themselves in weren't interesting enough for the setting to suffice as a backdrop (as is the case with "great" scifi IMO). E.g. questions about residual population size, effects of inbreeding, the actual goal of Silo 1 (why program the nanobot cloud just to enshroud the silos – did Thurman nuke/nanonuke the rest of the world too?). The diggers are literal dei ex machina, but that's nothing to lose sleep over.

Book three is coated with dramatic irony. It opens with Don who is dying and intensely focused on his and Charlotte's immediate survival via maintenance of the lie that he is Thurman, working for/with/agains Juliet in 18 who is situated with far less power than he, but is focused on the survival of everyone.

This dynamic develops throughout the book as the turntables do their thing, and the foibles required by ~plot unfold with painful irony.

The theme of mortality is further developed (or at least gets lip service, I guess) with a conversation between Lukas and Juliet about what is intransient; what is immortal? Lukas offers the suggestion that only our decisions are permanent. Juliet contemplates the immortal grammatical tense of "I will always have had done something." Additionally, Donald has the thought that no lives are ever truly saved, just prolonged.

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