I do know what you mean about caring for the characters in a novel. There was a book or series that is so forgettable that I don't remember title or author. I need to feel something for the characters in a book, movie or TV show for me to care about the plot. I wouldn't write of Grisham for one turkey.
Here's a review from Amazon that seems to agree with your take:
http://www.amazon.com/Gray-Mountain-Novel-John-Grisham/dp/038553714X/ref=sr_1_1?s=books&ie=UTF8&qid=1423057446&sr=1-1&keywords=Gray+Mountain
Retired teacher
By Reader on October 21, 2014
Format: Kindle Edition
Always a fan of John Grisham for his finely etched characterizations and ability to draw the reader into the courtroom drama of which his books are based. This book reads more like a docu drama. I did not like Samantha the female protagonist, who seemed a flat cardboard person who is self absorbed and shallow....bored with her job in a big law firm until she is unexpectedly let go due to the stock market crash. Then she is introduced to a world of the Appalachian "real people" through her volunteering at a free legal clinic and consequently becomes aware of many issues involving hardcore poverty and the huge environmentally devastating coal mining industry. Do not expect an armchair reading the usual Grisham novel generates....I put it down several times tired of the characters and being preached at about a thinly veiled attempt to spread the word of governmental collusion with the coal industry.
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