I don't want to say too much about this book. It is the sort of book which I think will speak to each person in different ways, and I don't want to put a frame of reference on it.
I really enjoyed reading it, I read a lot of technical books, a lot of other hard to read books, and I found this just a perfect breather in between them.
The main message that stands out to me from the book, is that there are many ways to "enlightenment". Of course, what is enlightenment, and is enlightenment even necessarily a good thing? Is it good for ourselves? Maybe, but for the world?
I wouldn't read this book to gain an understanding of what Buddhism has to say, if you are looking for that then What the Buddha Taught which I reviewed earlier, would be a good precursor to this classic.
Read this to spend time with yourself. Read it sitting next to a river if you can.
Note the is also an audio version at Librivox: https://librivox.org/siddhartha-by-hermann-hesse/