The third Dragon book is in my opinion the weakest of the three. The first two Asprin wrote alone, but his death 2 1/2 years before publication of this installment led to a co-writer in Ms. Nye, who he has worked with before on his MYTH series. Perhaps she was brought in on an unfinished manuscript. If so, she had a tough assignment.
Griffin Mc Candles is still running a small gambling operation in New Orleans, predominantly Texas Hold 'em, though in an instance or two it seemed the game ran slightly different from standard, especially with "turn and burn" cards. Knowing the game at least somewhat would help, as this book places the players at the tables far more often than the first books, especially Griffin.
Most of the book, especially the early part, runs well enough, though it does not seem to be coming to a point very fast, then it almost all collapses in - except in one major point, leading to hints there will have to be at least one more volume. It lost the flow, leading to the loss of a star and a half from a 4 star. Also, some inconsistency (Gris-Gris' uncle either changed names, or he has 2 uncles waiting tables at the same restaurant, the one we always saw, and this one) and some remarks about Homeland Security and their fictional agents in this book seem to be a writer's personal opinions thrust needlessly into the novel, lessening it.
My advice would be to see if a fourth volume emerges. If it does, and it is well reviewed, I would say buy both books, as plotlines DO continue and evolve in this book, but if not, I would skip this one. None of the major lines conclude here.