This is one of those books that takes me time to read because, well, it's a thick book, but more importantly, very dense.
It feels like a lot of this book includes thoughts from the author himself about Russia back in those days pre and post revolution, and civil war.
We follow a few characters from a young age, including, of course, doctor Jivago. We get to see them grow under huge difficulties, and... oh, what a life, their adult lives are no better!
We follow mostly Jivago, and the way he lives shows us in depth the harshness of life during those decades after the end of the Czars, WWI, the civil war putting Whites and Red under confrontation, and even WWII. We can see how initially people were so open about the revolution, but then how things got so difficult since there was an incredible amount of brutality, Russian against Russian. People lived in misery prior to the revolution, but things got no better after that. And along these terrible years we see Jivago's life entangled first with Tonia, his wife, later with Larissa, his lover, and also how the post revolution takes him away from some people, and again entagles him with others.
There is no joy in this book. None. It is sad, feels depressive, like a grey Winter that never ends. This book is filled with the brutality of people against each other and even the harsh Winters that made people's lives all the worst.
This book definitely needed some serious editing, as there is no need for it to be so dense. There are too many boring passages with religious topics, which I don't find interesting at all and add little to the plot. But I guess that portraits well the way they thought and lived back then. Many of the passages about the revolution and civil war are also too long and dense. They feel like they are appendixes to the story. Pages and pages where we don't even get to follow the main plot anymore. Just following the depressive life back then; the lack of food, the violence, the cold... 
I didn't like any of the characters either, didn't engage with them. I felt like I only got to know them superficially. They all feel depressive, like the weather.
With that being said, despite this being a difficult book to read, it is at the same time a great chronicle that portraits really well the difficulties and brutality of the time. What people believed in, and fought for, how things changed over time, how people made enourmous sacrifices to stay alive, how they accepted that life is harsh. But they live with few moments of joy, and everything feels, well... depressive.