‘Serious’ is an inadequate word. I wish I could find another, but ‘sincere’ has been murdered by President Nixon, and ‘authentic’ by the fancy critics, and there is no adjectival form of ‘integrity’, which is the quality I am talking about. Integrity, plus intelligence. An author who thinks out a major subject thoroughly, who feels the subject intensely, and who talks about it clearly, that is what I mean. The word ‘clearly’, of course, does not imply logic, expository prose, naturalism, or any other specific device; clarity in art is achieved by means that suit the end in view, which may be extremely subtle, complex and obscure. The skilled use of such means is the artist’s art. And the use of them involves considerable pain.
— Ursula Le Guin (via here)