Rufus Sewell, so often cast as the scenery-chewing bad guy, gets to play Aurelio Zen - an Italian detective accused of "scrupulous honesty" ("a horrible slander," as his boss puts it). I don't know if the credit here should go to Michael Dibdin (the book author) or the BBC's writers, but the story is beautifully constructed and as a result a joy to watch. We walk into this with no knowledge of Zen, but watching him around the office quickly establishes his personality, his past behaviour, and the behaviour of his office mates. And while he's run through a political wringer that establishes the case he'll be dealing with for the rest of the movie, we're learning more about him, his boss, and the politicians who are (trying to) pulling the strings, as well as the case: text-book quality writing.
Aurelio Zen is unusual in the Italian constabulary: he does try to do the right thing. Despite pressure from his boss and politicians. And it's stressing him out, but he's a smart and funny guy and Sewell wears it well. The movie was a real pleasure to watch, and the gorgeous Italian scenery didn't hurt at all.
The BBC did two more of the novels ("Cabal" and "Ratking"), I hope they're half as good. (They aren't.)