Firstly, the honest warning for anyone coming to read this book under the impression that this is a mystery novel - it is many things, but mystery novel it is not. More it is a philosophical, nostalgia-filled musings about purpose and meaning of life and love. Or silly and pretentious ponderings, if you are so inclined. I am somewhere between, honestly. Musings are OK for me, even simpler ones (as I find this book too be - its philosophy is only skin-deep for me), and (luckily) there are even some sharp, witty observations about people and life included that only Frenchmen can bring into the table.
The first part reads like an old adventure film full of Alains Delons and Jean-Pauls Belmondos. The middle part is heavier, but this depends on how much you believe in happenings and relationships like these. And the third part (which is the weakest in my opinion) depends also on how much melancholy vs. the cruel truths you are willing to bear.
I for myself adore this novel for the well-chosen quotes at the beginnings of every chapter. Also for some aforementioned observations. Yet, I do not believe the idea behind it (and what does not help is that I think the main heroine Gabrielle is a cow).
But really, reading the books as much is a very personal experience, so see for yourself.