I'm very much with Westwitch and JL Denny here.  The Wally Lamb book, "I Know This Much is True," is an awesome, elegant, heartbreaking look at mental illness, and the George RR Martin fantasy is adult, political, smart, engaging, fantastic, human, endlessly surprising, and it has SEX.  If yer gonna write for adults, you might just throw some sex in there so we can remember that it's people, not censo-bots, who are characters in the story.

But still, the very best novel I've ever read, is Sho-Gun by James Clavell.  The charactere, Toranaga, is the best-developed character I've ever seen...he is a full human being, and presented in fabulous complexity.  Open that book to page one, call me in two weeks when, red-eyed, late for work, and starving, you finally put it down.