An FPS where you have a gun, but there is only one bullet in it. So it is mainly an adventure game where you never know each time you play through whether the person you killed was the right one to yield the best narrative conclusion, or whether you should have killed anyone...
Every choice is different and the city in which this all takes place is full of characters who have individual motivations rather than fixed scripts, so your spatial-temporal interaction with all this leads to emergent behavior.
As this would, unchecked, potentially make the game impossible to get through and frustrating, part of the game engine creates a 'model' of your psychological state and gauges your ability for dynamically adjusting contextual levels of difficulty. It infers a lot about your personality by the 'quests' you undertake. There is no one story-line to follow, but there are consistently asserted underlying themes making it dramatic.