What makes Zombies, Run! cool is the zombie chases. While your music is playing a voice will once in awhile tell you there are zombies near by, and the distance away they are. If you keep going the same pace then the zombies will catch up to you. It's your goal to start going faster like go from a walk to a jog, or go from a run to a super fast run. You can also turn this option off if you live by a lot of stop lights, or you can pause the game.
I've only done one walk/jog with Zombies, Run!, but it was a lot of fun. I recommend it to anyone that has a love for zombie dodging, or want a fun way to get some exercise. You can get Zombies, Run! here for iPhone users, but don't worry it's also available for Android. Now I know it's $8, and you're used to your games being $0.99, but Zombies, Run! is worth the price!
image from their website