Getting There

The basic idea is to get from where you start to the objective on the other side of the map, with being spotted by undesireables.
Beginning: Each "New Game", you are dropped randomly somewhere with-in a reasonably large area (so repeat play & others gameplay is not always the same), with nothing. Somewhere random but close is a backpack (more on that later), a map & simple locator beacon system (more on that later too), and some health/food/water.
Backpack: All supplies have a mass & a volume. Your backpack has a finite volume, & the mass carried affects your stamina/travel abilities. Some supplies can be carried "outside" the pack (tagged as to whether they can or not), so volume doesn't matter, but mass still does.
Map: "Map" view is a split-screen, so you can see the world & map together. It is a topographical map, but DOESN'T show your position on it. It orients to the direction you are looking, & is zoomable. It is up to you to be able to read it. You have a simple locator system (not "proper" GPS), so you can drop a transmitter at your current location & put a marker on the map (these are separate acts; you need to know where on the map you are to place the marker) but once done, the HUD will show the direction to the transmitter (& signal strength, ie. distance (..ish)), and the mark stays on your map.
Terrain: A good mix of wilderness (open, forest, mountainous, etc), small villages, city to negotiate. Need to go down a cliff? Got to find a rope first. Crossing a river? Makes your boots wet which slows you down.
Objective: Again, randomly defined at a "New Game", always with-in a reasonably small area. Could be a port, hospital, "home", group of un-defined other people at a particular place.
NPCs: Both humans and animals, with only a few "beneficial" encounters (to gain info or supplies). Mostly, the idea is to not get seen or heard. Being spotted isn't an immediate "end game", but if you stick around you'll die. You can run, hide, distract etc. Human "enemies" are stronger & better armed than you, but you are faster & more agile (able to climb etc to places they can't follow).
Supplies: Randomly distributed at each "New Game". Important things (backpack, map, locator, "special" useful items like rope) always spawn with-in a reasonably small area. Some are "meta" ie. got to find a way to get into a shack to then find a shovel (or something).
Side quests: Besides simply "Getting There", there are simple side quests such as make it to the top of every mountain, shut off a broken water-main valve to stop a village flooding (& for you to cross it..?); things that are no exactly necessary to complete the overall quest, but still "fit".
Graphics: as realistic as possible (which is pretty damn realistic with todays game engines). Probably easiest to base it on a real-world location, for ease of creating realistic terrain.

I came up with this idea because pretty much all of the top "first person" games are "kill the bad guy"; I just like exploring the computer-generated worlds.