The story development could be improved. Most of the ads are voluntary for the sake of a reward, but there are also some intrusive ones. Some levels can be glitchy. A zombie may stand where you just can't turn to shoot them. Or your weapon will work fine for a majority of the mission and then just not fire on the last zombie, leaving you helpless. The world quests are not very developed story wise, but they are fun with the explosive bullets mods. These mods are not available in the story mode.