The one where the world gets darker, stranger, and more emotionally interesting. Time, fear, loyalty, and childhood magic starting to grow teeth.
Prisoner of Azkaban is where the world starts feeling deeper and darker without losing the school-year magic.
I liked the emotional shift: fear, memory, injustice, and the ache of family history begin to matter more than simple adventure.
The time-turner structure is clever and satisfying, even if time travel always walks in carrying a small logic grenade.
It is one of the strongest entries because it expands the world inward. More shadow, more heart, better magic.
The Dementors are such a strong image because they turn fear and depression into weather. That is fantasy doing its proper job: making something invisible suddenly stand in the room.
It also expands the emotional range of the series without losing the school-year charm. Still magical, still playful, but now the shadows have a schedule.