I am going to keep this review extremely short.
You will either love this book or you will hate it. If you believe in a higher form of spirituality, but aren't quite convinced about structure existing in religion, it may be a good book for you to read. If you do not believe in anything and think all 'spiritual stuff' is hokey, then don't bother reading this work. If you're a devout Christian/Muslim/Hindu/etc and cannot fathom anything that your religion does not teach explicitly, then don't read this book.
You should only read this book if you believe there is something else going on that you can't quite grasp, but are open to... or you believe you're currently in the midst of a spiritual awakening.
This book has some hokey elements in it - and I must admit to not believing in certain concepts by the author (especially those relating to 'what happened to the Mayans' - which I believe tarnished an otherwise great book), but I will say that The Celestine Prophecy changed my life. If you fit the criteria mentioned above, then I encourage you to see if there is anything in this work that can change yours too.
I should also mention that the writing in this work is not very good at all. It is all about the message and it's important to keep that in mind if you decide you wish to read it.
Since I have provided no summary, you can find one here: http://en.wikipedia.org/wiki/The_Celestine_Prophecy
To purchase the book, there are over 2,300 used copies here:
For those of you who give it a shot, good luck... and enjoy.