Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Meditative
Because this book is Nabokov's retrospective of his time as a kid and young émigré, he's had lots of time to think, think, think. Every event is held up for consideration, and even the quality of his memories (good or bad) are offered as evidence for his thinking about the nature of memory itself. Nabokov isn't just telling us his life story, he's offering his philosophies about the nature of time and existence.