Let's see. Extreme violence. Lots of explorations of madness. The RPG even warns the game is for mature audiences only in the front of the book. A literal demonic orgy at the beginning of another book. Explorations of the mind of a Chaos worshiper in another. Yet another orgy in another, but this one by elves. Exploration on themes of marriage. More explorations of death, friendship, sadism, gore, evil, incest, rape, cannabilism. One book is basically even Silence of the Lambs in the Warhammer setting.

So yes, dark, Goth, serious. Perhaps you're not familiar enough with the setting to realize this.