You really can't go wrong with John Grisham for a good read. Gray Mountain is no exception. I've read nearly all of Grisham's books and they're all solid reads that define the legal thriller genre.
Gray Mountain does for the coal industry what Runaway Jury did for the tobacco industry. Set in Appalachia, it gives a look at the local life, culture and natural landscape there that goes beyond the stereotype. In that respect, it's a brilliant and important book. He also takes on the new economy and Big Law, with pertinent glimpses into the moral and ethical conundrums that one can only hope all lawyers address at some point in their careers. The setting, characters and theme are all worthy of 5 stars.
As a Grisham fan, my only criticism is that - having read so many of his books - this one seems almost formulaic, like it's following a Grisham template. I would have liked to have seen a bit more originality, maybe a twistier plot, and potentially a stronger ending.