The Beginning:

The player wakes up on a after a plane crash in a forest, with no recollection of who he is, or how he got there. He needs to find out how he got there / what his purpose is.

You will have to investigate your surroundings further, in order to gain more knowledge of the location, and figure out the story.
The game is intended as a single player game, and some survival aspects involved with it. Those would be related to task such as find consumable items such as water/food to replenish health/hydration levels. Health could also be replenished by finding a place to sleep.

The HUD will provide indication on the health/stamina/water levels. The stamina level will be tied to how much effort you make – running/jumping.

Exploring – 

When you wake up after the crash, you do not have a map or any type of directions. In order to discover more of the location, and subsequently discover more of the story, you will have to explore.
Along the way you will meet friendly characters that will help unravel the story, as well as give you missions tied into the story.

The Town – 

You will eventually come across the main town area. This is where you will find many of the clues relating to you being here, along with the dangers that might get in your way. Explore, explore, explore.

You will have to avoid certain dangers, while taking others head on.

Wilderness – 

The surrounding area of the town will be a typical northern hemisphere forest, inspired by the Black Forest in Germany.

Gameplay – 

This will be a first person shooter / exploration game. All default movements that come with the engine will be available to navigate obstacles/terrain.
Stealth mechanics such as noise, distracting opponents, hiding, silent takedowns will be present.

When the player saves the game and leaves, they will pick it back up from the current spot. I am also considering a checkpoint save system.

Future plans / survival aspects for the game – 
The game possibly featuring a full 24 hour cycle.
You will have to hunt for food, either by setting snare traps, or by finding a way to create a makeshift bow.

Water will have to be boiled in order that you do not get sick. This also implies making fire, as well as not letting the fire die out.

Sickness symptoms of either uncooked food or water poisoning will include vomiting(with a dramatic drop in water level) and fainting(with a drop in stamina).

Exploring will give you the option to mark POI on your makeshift map (you never know what you can find in the trash). This way you can make it easier to find a water stream to collect water, or where wild critters would gather, for example.