Ok, this is quite ambitious so expect a wall of text incoming...
story: It's 2099. 50 years previously an alien race, driven off their home world by an expanding star, seek a new home on Earth. Records are unclear as to who threw the first stone, but within months a devastating war broke out. Both sides were fairly evenly matched. The humans had the advantage of numbers, projectile weapons (which had never been invented on the aliens home world), and prior knowledge and acclimatisation to the environment. The aliens however, had much sharper, much wider ranging sensory systems, were physically larger and stronger, and their genetic makeup also allowed them to absorb forces from the environment around them and turn them to their advantage (think super human abilities such as active camouflage, or breathing fire. The closest comparison would kind of be like the plasmids in Bioshock, crossed with the augmentations in Deus Ex, crossed again with Mass Effect's biotics).
The war lasted almost 3 decades, in which time both sides lost billions and the respective societies of both were all but destroyed. As it became clear to both sides that neither could possibly achieve an outright victory, a ceasefire was reached. Now human and alien live in a mostly peaceful (but sometimes still uneasy) coexistence on the 45% of the worlds surface that has been left habitable after the war. Language, culture, and technology are now largely mixed, and in some of the most tolerant ares their are even some 'interesting' hybrid species emerging as a result of cross-breeding. The world of 2099 has similarities with the Old West. Civilisation and order are starting to reappear after the anarchy of the war, but chaos and violence are still commonplace. It is a world of infinite opportunity, but equally infinite danger.
You are 'The Traveler' (species, gender, appearance are created by the player. You real name and origin are unknown.) You goal (this is where it starts pushing the envelope), survive. That's it. There is no central plot. You are given this vast world with thousands of opportunities and thousands of individuals to interact with. How much (or how little) you make of it is entirely up to you.
gameplay: As I just stated, 2099 (I've just decided that's what I'm going to call the game) is the last word in player choice and variation. It includes a wide variety of different gameplay elements. If you choose to play it as a combat game the majority of it is in first person, but you will be able to switch to third person to give a more tactical/stealth feel when required. The combat is designed to blend gun play and melee seamlessly, with the inclusion of the alien abilities (which are gained by injecting yourself with various formula's of alien genetic material if you play as a human) mixing the familiar shooter feel up a little.
If you choose a less violent path the emphasis on social interaction (there is no moral choice system. While there is choice running through the whole game, what the correct action is is your choice alone. You won't be compelled by the game to always choose the 'evil' option just because you need the 'evil' points for your 'evil' playthrough. This is the new wild west, who can tell what's right and wrong in this world), as well as management, RTS and life-simulator style. All this is heavily laced with RPG elements. However, progression isn't necessary, just another option. If you want to always stay near the bottom of the food chain in whatever you do, you can.
You night ask "Why would you be content to never really progress in the game?". Well, the engine the game runs on operates around the central theme of probability and random events. There is no 'end' to the game. When you complete challenges the game simply engineers new scenarios to create new challenges, and these will depend on your position in the game. If you fight your way to the top and play king you have a larger game experience, but you have to watch your back, as they'll always be something trying to knock you off your throne. Alternatively, if you decide to just run a small business within the game world you are more limited, but the chances of you putting yourself or your NPC companions in danger are slim.
Game developers talk about playing the same game but choosing different paths often. I want to take this concept to the extreme. I want to create a single game where one person could be a tyrant, another a mercenary, another a carpenter, another a diplomat... and so on and so forth. I want the possibilities to be a close to endless as is possible and I want the game to last as long as the player wishes it too, not the developer.