Major spoilers! You've been warned...
So Karen dragged me to this monstrosity (pardon the pun) tonight, and while it was definitely two hours of suspenseful action, the movie frustrated me to no end.
First, the zombie plague itself. I'm willing to accept zombies as a supernatural phenomenon (ala Dawn of the Dead) or as a medical phenomenon (ala 28 Days Later) but not both. The movie heavily implied that zombie-ism was a disease communicated by the bite of the infected. Fine. But to have the infection cause a person to turn into something that looked like a two-week-old dessicated corpse in the course of ten seconds - well, that's a little odd. All infections, even in the blood, take much longer than that to be fatal.
Then there's the way the zombies move. They're fast and strong, but the movie states that they have no circulatory system and they don't appear to eat. That's just not possible. There's a reason all animals have an aerobic metabolism. You need to oxidize fuel quickly to move quickly. The zombies appear to want to bite, but not eat, which makes no sense either - they're going to need something to fuel their evidently limitless energy.
And their behavior is clearly predatory, but not in a way that makes any sense. We find out (major plot twist!) that they don't like sick humans - they just ignore them. Which makes sense (maybe) if they were trying to pick out healthy individuals to convert. But since the infection kills instantly and the zombies, once turned, are nearly immune to massive physical damage (up to and including breaking their limbs and spines) what does it matter if somebody had a bad flu before they were turned?
Then there's the whole "how do you kill a zombie?" thing. They go down to bullets - at least at first - but we're told that body shots just slow them down and it takes a head shot to "kill" them. That seems to apply through most of the movie, but we also see a corpse that has been burned to ash except for the fingers which are still moving. Forget for a moment that the tendons and muscles necessary to move those fingers have been completely carbonized - if taking out the head "kills" zombies (and again, it does in many other scenes) then what's going on there?
The last bit of bogus biology is that the zombies don't appear to "wear out" - despite having no circulatory system (and therefore no functioning immune system) and despite neither eating nor drinking, they appear to be able to exist indefinitely in, for example, scorching desert conditions. In reality, any zombie subject to the laws of physics and biology is going to have a rather short shelf life.
Finally, let's get back to the whole turning thing. You're telling me that an infection that can be transmitted by a superficial bite can, in the span of ten seconds, convert a human body into something that looks like it's spent days decomposing and change its metabolic system so that it can move quickly without oxygen and give it a completely new set of instincts that makes it a predator of humans that can navigate by sound but also somehow magically know when a person is sick or healthy and give it the instinct only to bite, in order to spread the disease, but not to eat or damage its victim in any other way?
I'm willing to suspend disbelief, but there's only so far. World War Z entertained me, yes, but not nearly as much as it pissed me off.