As they advance their survivors' stories, players come across new quests and individual targets, leading them to gain influence. Who comes out ahead depends on how keenly and aggressively each player ventures through the game; however, if a single faction is pushed to power too quickly, the wasteland will be taken for their own, and the survivors conquered along with it.
Each scenario has distinctive landmarks — e.g., The Capital Wasteland, The Pitt, The Commonwealth, and Far Harbor — but otherwise the map is variable, with players exploring the terrain and (ideally) avoiding radiation to uncover equipment and do whatever it is they want to do to gain influence.
FFG lists a release date of Q4 2017 for Fallout, but perhaps the game will be on a few demo tables at Gen Con to give attendees a first-hand taste of how the game plays out.
(Note that this is the second Fallout title due for release this year as in April 2017 UK publisher Modiphius Entertainment announced the Nov. 2017 release of Fallout: Wasteland Warfare, a minis-heavy design from James Sheahan. Modiphius has confirmed that title as being available for demos during Gen Con 50, so perhaps we'll have head-to-head Fallout fever to see which games best survives the fire and fury of fans.)