I did the first Zombies, Run! run last night!
So, the way it works basically is that you are a character in a story, running from zombies. You get little snippets from other characters ("run to the hospital and pick up some medical supplies!" etc) and you also collect random things as you run. You can play your own music while you run and the app just cuts the music out when it's time for a snippet of story...if that makes sense. You can set it to be however long you want. You can also turn on "zombie chase" mode where you get randomly chased by zombies every so often, so have to speed up, but I had that turned off for my first run.
I really enjoyed it! I struggle to listen to podcasts while I run but get a bit bored of music and this was just the right balance to keep me interested and motivated. I even sped up at the end when the zombies were chasing me to the gate! 
@sovielverloren - I'm totally the same, apped up to the max! I get really motivated by recording and tracking. I used to use MapMyRun but I have a Fitbit now and use that instead.
I haven't heard of Beat Beethoven but it looks like a great idea! I have just signed up for the Vitality Running World Cup, where you have to run 3k in 30 mins and you represent your country, like any other world cup. It's good to have something to focus on.