This was the fourth or fifth book by John Grisham which I read. And I was sorely disappointed. None of the thrill of the Pelican Brief, none of the legal tangles of The Firm, none of the hard core cynicism of The Brethren.
The Testament reads more like a travelogue into South America, since the details of the journey overshadow the legal aspects of the book. The explanation lies in the authors note -- the fact that the author went into Brazil with his friend, Carl King. The book is thus more of a tribute to his friend, a Baptist missionary.
Besides, the lead character of Nick is too dark. His failings are emphasised too much. I feel the character is not all balanced.
Hence, I would suggest that if you have never read Grisham before, dont start with The Testament. Start with one of the others. Once you are familiar with his work, you may be willing to forgive him for writing The Testament! Like I did.