For me, fast vs slow zombies depends on the type of movie. In a genuine horror movie I need fast zombies. The threat isn't real enough with slow zombies. But if the tone is lighter, than slow zombies work better.
A movie like Versus, the zombies are slow enough that everyone is trying to look cool as they kill them.
But a movie like 28 Days Later works as a great horror because the zombies are such a terrifying threat, endlessly chasing you down at speed.
The Walking Dead doesn't work for me because I don't see the zombies as a genuine threat. You can power-walk away from them. Slow zombies only really work in a confined space such as a shopping mall.
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