This was one of the hardest book I've read and bear in mind that I've read the first edition many years ago. It took me a few months to read it cover to cover, mostly because I wanted to play with concepts presented and explained in the book. Sorry for whining, but I really enjoyed the proccess of reading, hence this sacrifice of reading one chapter and even less every week was absolutley worth it.
At first I expected it to simply copy concepts from the previous book and add features of more recent JVMs as Joshua Bloch does with "Effective Java". I was utterly wrong.
This book is a complete redesign having not much in common with the first edition. Most basics like explaining how the classloaders work in Java (that are mostly unneccessary for experienced devs but may be needed for the newcomers) are gone now. The book is really condensed and purified now. I was often finding things I had no idea before while reading it. And I'm doing Java for more than a decade now, though I had breaks to work on other languages to learn to see things from another's perspective. It allows me to be multifaceted to a degree where I can choose whether to use Scala, Ruby, Golang, JS or Java to implement a certain feature. Offtopic aside this helps me a lot to understand how the JVM works and I can compare its implementation of certain features with other languages and compilers.
This book is a real pleasure to read though it requires a lot of thoughtwork from the reader if you want to get bang for your buck.
I'd put it on one shelf with "Effective Java", "Java concurrency in Practice". This book is a must have for anyone who wants to advance in his career connected to the JVM.
My score 5/5