I've got this crazy opinion that some may not agree with, but hear me out:
If zombies are in a game, the chances of that game being good are better than the majority of games out there. This is because zombies are the coolest thing in the world. Even cooler than ninjas. Zombies eat brains. They can be fast or slow. They are hard to kill unless you are a good aim or have a good melee weapon. They are just, in general, fucking amazing.