Fiction is like dreams: a fanciful way of symbolically articulating and experiencing our innermost thoughts and feelings. To thrive and prosper in reality we must struggle, hence, the everlasting relevance of adventure stories. The "hero" of such a tale is the champion of our struggle. The "villain" is the will that opposes us. A "monster" is the primal forces to be reckoned with.
Adventure must be exciting if it is to be adventurous. Danger must lurk if a hero is to prove heroic. A villain must mean harm if he is to be villainous. A monster must prey on humanity if it is to be monstrous. The story is one of effort and conflict. The characters and their interactions are the story.
Fighting is what makes an adventure story intense; mortal combat specifically. Peril and sexuality can do much to excite but violence is a must. The struggle is the very theme of the adventure. It resonates because we all struggle. A battle to the death is the ultimate clash of wills. Fighting to the death, inside or out, is a tribulation we all face just by living.
Adventure fiction easily assimilates every other genre... because questing and conflict are the defining moments of the human condition.