I like the high number of zombies. And it would be bearable if they weren't allowed to run. Perhaps a zombie that recently killed someone would go into a running frenzy. But what I personally love about zombies is that they are generally slow, stupid and rotting. Rotting muscles don't move so fast. And that their strength is within their numbers. Their ability to horde and swarm you. The fact that their numbers are greater than your ammo. I pretty much share Simon Pegg's opinion on why Zombies Shouldn't Run: http://www.guardian.co.uk/media/2008/nov/04/television-simon-pegg-dead-set