Along with the main quest, you may explore buildings, ruins, and caves of the post apocalyptic city in order to gain better equipment and items,you may level up your character by killing lots of zombies (Fun), you may build a fort anywhere you choose and hold off against the hordes of zombies, you may also enlist the help of AIs or other gamers in multiplayer (yet to be determined if multiplayer or controllable AIs will be used), or you may do a combination of any of these strategies or most likely all of them. 

The challenge of the game comes with the fact that not all of the region you are in is visible all of the time. Remember that it is a 2-D aerial view game. Now imagine you are looking from the birds eye and see your character with a flashlight like cone of visibility in front of him and a smaller circle of visibility around him, this is the perception of your player and will be effected by the available light (darker rooms = smaller perception cone, brighter rooms = bigger perception cone). Items such as flashlights and leveling up your perception level will increase how much you will be able to see. Although, it is not pitch black around the perceptive cone, it would work a lot like fog in a RTSG, you will know the map but not know if there are enemies in an area. The other challenge that comes with this game would be the constant zombie horde attacks, there are no rounds or main menus to buy items like in "Block Head Arena" or "Black Ops." instead there will be significantly fewer zombies in well lit areas than in pitch darkness, so you must take advantage of the safe time you have to set up shop and defenses. 

This is NOT a tower defense game it is a free roam quest finder and completer. 

The replayability of this game is that after you kill the mother zombie once on normal mode you then can advance to hard mode for much higher chances of better loot, and then again on impossible mode for the same benefits of better loot. Multiplayer capabilities could be another factor of replayability.  

Please take the time to view the power point for any info that you may have missed or that I was unclear about.

Please comment and inquire further on my game. I am open to any questions and suggestions and I am always looking for help on the game. I need a strong programmer presence but I do not require a strong designer presence, save the pro artists for bigger games. I'm just doing simple 2-D art.