I consider "fast zombies" to be an oxymoron.And I much prefer fast zombie over slow ones.
As for this movie, I'm with Umbran - I would have loved to have seen an actual adaptation of the original novel, and I'm kind of ticked that by basically stealing the name "World War Z" and grafting it onto a movie that is in no way, shape, or form anything like the novel "World War Z," I'm not likely to ever get to see a movie version of the "World War Z" novel. Which is a shame, because that was an excellent book, and it could have been an excellent movie. Part of the appeal is that it's such a mosaic; this is definitely not a story that should revolve around a specific, "star" character.
Oh well. Plenty of other movies coming up that look interesting. "Kick Ass 2" is out in two months; hopefully that will be good.
Johnathan