I saw a reference to Bioshock and Fallout 3 and I got interested really fast. I thoroughly enjoyed the Bioshock series and I have been a huge fan of the fallout games (and RPG's in general). Would love to contribute to it, but the starting teaser is all I know about for now.
I have always believed that a game lasts and lasts when replay-ability is deeply explored. Even though, when we consider the elder scrolls we can join anything, I believe that limitations can make a game last a lot longer (i designed a partial story line for a Skyrim successor).
A game should give the option to explore the antagonist and the protector side (good and evil), yet you must allow for freedom to truly explore choices and many options would be grey (they become boring if they are utterly black and white).
the story should always be more then the main line and the side quests. I believe that a pool of both could fuel replayability, making a 200 hour game a legendary 1200 hour game, whilst not having to include 600% of data. To give an example, we should consider Diablo 3, where the person will not always have access to certain locations. We know that comes quests come from performing some earlier quests, but what happens if we only allow 15 of the 50 quests? What if the side quests, come from the chose 15 options and also depends on the outcome of what we did there?
The previous contributor (BenPonder) states something interesting "Who fixes the hidden cameras and microphones when they break?" that is actually a good question, when we consider most RPG's we get the fighter, the wizard and the sneak (assassin/thief). What if we take a look at one of my all time favourites (System Shock) where we see the soldier, the adept and the technician. We can see more power if we consider the We Happy Few trailer, the Policeman, the politician and the janitor, whilst all are also part of the population. an RPG, where the policeman can evolve into the controller and overseer, the media-man can become the announcer and the janitor can become the engineer. three distinct paths all giving access to different places, whilst rising in ranks they will give access to all lower places. They also have perks, the Janitor is a better repairman and can facet stronger weapons, the policeman can manage security and access, the media man can rally troops and talks him/herself into many places. as the janitor evolves, he/she can also influence locks and camera's, whilst getting access to places and doors and so on. It allows for a preferred playing style whilst accommodating gamers to try alternative styles (because of unique quests).
In all this it revolves around the story-line, which would only get stronger as we see other sides of that same story.
Just a few thoughts to consider.
Looking forward to this game!