I remember reading an interview with the great director Sidney Lumet, who died this weekend at the age of 86, in which he was asked if he had a particularly identifiable style.
No, he said, because he believed every story had a particular way it needed to be told, and his job as director was to find it. As example, he cited one of his best-known movies, Network. Many scenes he chose to shoot in an almost verite style, the better to establish the reality of the world he's presenting. He realized, however, that certain individual scenes would seem ridiculous if shot in a naturalistic manner. So these scenes have their own style, whether over-the-top flamboyant, or rich with the shadowy menace of classic noir, or whatever.
The trick was deciding how far to push these individual scenes for maximum impact while not allowing the different styles to clash with each other, to make sure the film stood as its own fully-integrated entity, not just a collection of scenes. And if you've seen Network, you know Lumet more than met his goals. You can dislike the movie itself, mostly due to Paddy Chayefsky's declamatory script, but it's impossible to quibble with Lumet's handling of it--purely as a piece of filmmaking, it is absolutely brilliant.
As was so much of what he did--Twelve Angry Men, Serpico, Dog Day Afternoon, Prince Of The City, Before The Devil Knows You're Dead. He was incredibly prolific, and he made a few also-rans, as well as a number of outright losers. (If you have a few spare hours sometime, ask me what I think of The Wiz.) Good, bad or great, everything he did was the work of a man who above all had the intention of telling you a story. He was something rarer and more valuable than an artist. He was a professional.