I dunno if we need go that far to call a D&D book, "mature". I would say normal level World of Darkness be about equal with what be considered a "mature" D&D book. Now how that maturity is handled in either case of course changes.D&D just isn't the game for it. When Wite Wolf did it back in the nineties with Black Dog (I think that was the label) it at least fit the themes of the game.
Over the top violence and gore? That's just plain D&D for us.
Erotica? Ummm---no thanks.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.