The Secret Garden is a joyful and passionate tale of childhood reliance, relationships, and healing. I felt consistently through the book as if Burnett related to the children he wrote about and due to this, he manages to carry an air of mystery and childish glee throughout the story without making the characters feel particularly 'young'. Their intelligence and personalities felt authentic. 
The ending was surprisingly abrupt which I found disappointing in comparison with the vast descriptiveness and detailed telling of the rest of the book, but there was something rather playful about it, which made it feel like a purposeful choice. 
There are moments of racism in the writing - mostly concentrated at the beginning of the book - which take you jarringly out of the story. I found the casual presence of such passages uncomfortable to read and acutely poignant against the setting of a warm children's story.