The Saboteur
There are main story missions and side-missions. When you complete a key objective, such as blowing up a special Nazi weapon or killing a key Nazi, that specific section of the city gets liberated from the Nazi oppression. The advantage of doing that is that it makes it easier for you to escape the Nazis when they are after you. Without spoiling the storyline, unless the game is too hard for you, you can just ignore those side-missions but completing them can sometimes liberate a part of the city, making it easier to escape the Nazis.
Read More