Contested Sequel: Some fans like how Dust brings the plot threads and characters together for a more definitive ending. Others loathe and/or disregard the book for having a forgettable and underwhelming climax, killing off many well-liked characters from previous books, and having to bring the Big BadBack from the Dead in an Ass Pull manner to even have an excuse for the conflict that drives the plot and causes those controversial deaths.
Nightmare Fuel: IT has been sabotaging the cleaning suits for decades. Every person sent out to clean before Juliette could have survived, but IT deliberately swapped out the suit materials for faulty ones. The IT department is literally playing executioner.
Primal Fear: Loads: claustrophobia AND agoraphobia, fear of the dark, sense-loss (by wearing thick blinded space-suits), asphyxiation (especially by choking on your own fumes).
Squick: Solo's living conditions. For example, the toilets have stopped flushing in his Silo, so since Solo's the only one around, he just uses a bathroom until it gets disgusting before moving to another.
The Woobie: Solo, who is 50 years old and has been alone since he's been 16. Mentally, he's still a (smart, shy, kind) little kid.