Tokyo Ghoul begins with a shy bookish student going on a date with a girl who turns out to want to eat him, and an accident that leaves him half ghoul. Everything after that is about a person who no longer fits in either of the two worlds he now belongs to.
Sui Ishida's central idea is that the ghouls are people. They have cafés, families, grudges and jobs, and they cannot eat anything except humans, which makes the moral situation genuinely unresolvable rather than a matter of good and evil.
The masks are the series' visual signature and they exist for a practical reason - ghouls need to hide their identities from investigators - which makes them character statements rather than costumes.
Kaneki's transformation across the series is one of the more harrowing character arcs in the medium, and the interrogation sequence in the first season is the moment it announces what kind of story it is.
This collection covers Kaneki, masks and kagune.