Storyline Development

I've began to compile the overall storyline of my game, including how the levels will flow into one an other such as moving from your car wreck to a supermarket for medical supplies before leaving out the rear exit and searching for a gun store for ammunition. I've also finalised the details on just whats causing the zombies to begin wandering about along with the details of how the story is introduced using New Reports. I've felt that keeping the main character a mystery for the first few levels may act in my favor, creating another reason for people to continue to play, to find out more about the character and the overall storyline. I thought about putting some sort of timed aspect into the game, but I felt that if I had included that it would become tedious for some, making there way past a hard part just to find out they wont have enough time to actually finish the game. I'm still working on a good leveling for the character as I wanted to have some of currency but feel that for each kill you gain 1 XP point, to begin with it takes 5 points to upgrade one skill, 10 to upgrade it to level 2, 20 to level 3 and so on, and perhaps people could take a leveled character back to the beginning to continue to level it rather than tarting from the beginning with a new character each time actually give them something they can actually improve.