As we are all aware, Osho was a former lecturer of philosophy and was quite a good orator.
But, he often used his extensive readings on various topics as his discoveries!
Undoubtedly, this fact often irritated everyone- philosophers, seers and devotees.
This book is nothing but sum up of his readings on Kundalini- a great subject of discussion among hindu and buddhist monks.
Osho simply presented what is presented in Gorakh Rahasya and buddhist tantra classics and made his "teachings" to his western audience.
So, in my humble view; this is not a great book.
On the contrary, I wish all to read views of Swami Muktananda of Ganeshpuri, Milarepa(a buddhist tantra guru) on this very deep and enchanting subject.