The best directors are those that have a world view that informs their work (we expect it of composers and painters...why not filmmakers?).  They must also NOTpander to the public.  A Beethoven (especially in his later work) and a Picasso never gave the impression that they cared about the "public".  They did what they HAD to do.

There are few directors of film that follow these rules.  

Spielberg panders all the time because he wants to be loved.  Kurosawa attempted suicide in the early '70's because he was out of favour in Japan.  Coppola (a good director) would rather make wine than make personal (if unpopular) films.  Are these people artists in the truest sense of the word?  Perhaps!

But...I would rather watch a bad, but heartfelt and personal film by Altman than anything by Spielberg.  I'd rather watch a flawed, but deeply humanistic film by Renoir, than the later work of Kurosawa.  I'd rather laugh at one of Buñuel's "hack" films from Mexico (say THE GREAT MADCAP) then "Jack" or "Bram Stoker's Dracula" by Coppola.  And...I would rather watch any film by Michael Powell, Orson Welles, Stanley Kubrick, Chantal Akerman, Ingmar Bergman or even (more recently) Brad Anderson, then just about anyone else out there.  They are true "originals" who are making or have made films that they HAD to make.  They never leave the impression that their films are "just jobs".  They truly care about their characters and their stories and their films, although often "unsuccessful", are truly heartfelt.