I'm supposed to be doing my first mission where I have to kill some gunning lunatic in the food court, but I decided to just ditch him and ran back outside, grabbed my car and started running down more zombies. Killed about 5,000 so far (I'm amazed at how many can be on the screen without lag). I'm also getting easy level ups this way. Hell, I can spend all 7 hours they gave me just running down zombies and leveling up, that way I can keep my character and start a new game and be all uber.