Add the ability, when every time if you change clothes, you change a first-person view also! For example, changing the character of a glove or jacket, changing the type of holding a weapon, knife, etc.
Add the ability to build something new, shelters (on the surface) or a small house.
Add the ability to cut fresh trees.
Add new threats. Varieties of bears, wolves, elks, in each location should be completely different from previous ones. Each location must have its own behavior for animals. Not like the rest.
Add a new animal, such as birds. Let it be possible to eat their meat.
Add the ability to carry things, let the bag hold more KG. Or you need to add a wooden sled.
MANDATORY, add the ability to automatically get out of sleep, with the risk of frostbite or hypothermia. (all the time I died only for this reason)