What I've noticed is that most character actors like Walter Huston, for instance. Well I shouldn't compare him to Walter Huston ::)
But what I've noticed about Quentin is that he doesn't have the posture or the voice to really transform into another person . I feel that he is too rigid. Mainly because he is acting to his own writing, and his writing is close to his personality, so when you see him act, you're just watching Quentin behaving differently and not acting.
A real character actor just transforms right before your eyes, ,and you just know when they are good like Richard Burton in Who's Afraid Of Virginia Woolf.
-Notice that great writer/directors who acted have a great posture and voice. They stand out in a very good way.
John Huston, Orson - these guys were REAL character actors, and they were able to become other people.