This is a cool book, and series, and all that, but I'd really like to see them film Philip Nutman's novel Wet Work
. That has different 'stages' of undead, if you can believe it; some of them are the slow, shambling 'dumb' zombies we're used to seeing, others are the super-fast variety, all the way up to intelligent, thinking zombies that retain their personality and memories and can do everything we can, like talk, drive cars, put on new clothes, organize ambushes ("Body patrol, come and bag our food!") using guns, etc.
Failing that, I'd go for the possessed-by-aliens angle that another book (which I can't remember at the moment) used. I think that's the only actual 'realistic' zombie portrayal that could be done. There's no other way a dead body could become reanimated; biology just doesn't work that way.