This is the second film adaptation of one of James Lee Burke's Dave Robicheaux series, the first being "Heaven's Prisoners" with Alec Baldwin horribly miscast as Robicheaux.
In this film, Tommy Lee Jones is perfectly cast as Robicheaux, capturing all the nuance of the literary character: the alcoholic obsessions, the need to impose justice, his essential toughness and goodness.
This is a pretty faithful adaptation of the novel, and captures the flavor of the books, as well as the Louisiana settings. In all honesty, this was almost exactly how I'd pictured it from reading the books.
But a caveat: if you haven't read the books, you're probably not going to enjoy this movie, which is probably why in the USA it was released directly to DVD. Burke's novels are very introspective, which makes for interesting literature, but slow movies. There's plenty of drama, with several murders, corruption, and depravity to spare. But the books - and this movie - are at their hearts character studies of the Robicheaux character. This is more akin to "Smilla's Sense of Snow" than "Dirty Harry".
I loved it; your mileage may vary.