One of my favourite things in media is when the story follows the entire lifetime of a character and looks at how their personality develops over that time - this is the epitome of that. 

You really get to know the three siblings the book focuses on - their weaknesses, their fears and anxieties. Nobody, even side characters, is two-dimensional, everyone is complicated and self-contradicting. The book also doesn't feel the need to explicitly explain every character, like others would - like in real life, people stay opaque.

Perhaps, for my liking, it was a little too sad at times, especially when it came to topics like death - but I think you're going to have to accept that an author that writes a book like this also thinks about death or how good life is in kinda negative ways.