I actually thought this was brilliant, easily the most dangerous and terrifying take on zombies, the stuff they can do is mental. Slow moving zombies and even the fast ones from 28 days, in real life (in my opinion) couldn't stand a chance at world wide infection, all the zombies would be killed at some point. These kind though? The formations and flood like movement is so effective, it's believable that the virus in this could bring us close to extinction.
8/10 easily.
You need to read the books, so much better and so much detail.
Was disappointed that they didn't even explain zombies or half the cool big scenes in the book, many of which could have easily of been incorporated in the film.

.
.