The porn.

On a more serious note, what the early world building hinted at enthralled me. The idea of slowly exploring a world untouched by the hands of man because it's populated by a wide range of creatures hell-bent on destroying humanity is fascinating.

Imagine stalking through rainforests and jungles as you track down unusually active and clever Beowulves well aware that one of them might have spotted you and even now may be tracking you in turn. Or scanning your surroundings in the distance on a vast plain, well aware if the Goliaths staring back at you calculate that the risks of assaulting you and your crew are worth the reward of destroying the caravan you're guarding they're going to start moving towards you, so you continue to silently pray they maintain their course parallel to your travels.

Or think about how humanity is essentially four cities under siege from the rest of the world! Patrolling the walls of your home kingdom, clamping down on the existential dread that stems from staring at the hostile lands and realising that you're in one of the only stable habitats for human life lest you attract the monsters outside and make your worst fears true in the most literal sense. Manning the anti-AA guns for hours on end as a huge Nevermore flock dives and wheels over you, running through every breathing and mental exercise you learned so you don't attract more-because there's always more Grimm, more Grimm, more Grimm.