Gwi-nam is a great villian. I love it (and hate it) when someone can scare the s*#t out of you by just making a neutral face or even smiling at you.
Christoph Waltz as Hans Landa in Inglorious Basterds is someone like that: Smiling at you and talking gently while every piece of your body cries "RUN"!
The performance here is also great and the story is much better with such a "supervillain" than just with the normal zombies.
They can always outsmart the zombies but there is still Gwi-nam...