I am loving the game and the atmosphere can be great at times especially when you get the strange creature sounds in the background, what i thought could be cool is world monsters that pass by off screen or in the water that you can not do anything with but there shear size and power to make you feel that your not all powerful and that there is always something bigger and darker moving around you that you are powerless to defend against.
You could even do it as mini events where you have to run and escape from a world monster and at the same time monster start to spawn all around you as if to slow you down until the monster can have its meal.