One of the reasons I was so surprised that the recent World War Z trailer didn't use the word "zombie" at all is that I had in fact already seen the movie, and lines of dialogue featuring the z-word were actually stripped of it to show in the selected clips. Whatever the reason for the movie marketing being so vague, rest assured the movie is not. They say it, and the creatures act like it...more or less.
World War Z's most significant and controversial departure from the book is to have "fast zombies" - but for those who feel that the movie can be its own thing, they're the film's biggest plus, as they're a new take we haven't quite seen before. They don't just run - they snap, crackle and pop their bodies while transforming, then behave like living weapons once it's taken hold, smashing their bodies into glass until it breaks, and even deliberately falling off roofs to get the people below, regardless of how many bones they break in their own infected bodies. These are zombies as suicide bombers - perhaps as metaphor for enemies we have a hard time fighting, but more likely because somebody said, "Hey, you know what I'm scared of? Suicide bombers. Let's combine them with zombies."
Are they even zombies? We're still arguing that about 28 Days Later, and these too are caused by a virus, one described as rabies-like. Live victims who turn seem never to have actually died, but the dead can also revive, and the infected don't die for good until destroyed utterly (even then, one wiggling toe might keep on keepin' on).
In an attempt to duplicate the global scale of Max Brooks' book (and little else about it), former U.N. investigator Gerry Lane (Brad Pitt) is forced into a wide-scale search for Patient Zero, which takes him to Africa, Israel and the U.K. He's forced into it because even after it's made clear that humanity will rapidly become extinct if things continue as they are, he initially refuses to leave his family, because duh, he's Brad Pitt and they're more important than everyone dying. Until the army threatens to have them kicked off the boat on which they're sheltered.
This is symptomatic of the movie's biggest weakness: Lane's family sucks. Director Marc Forster (Quantum of Solace) dwells on them way more than he should, too. The filmmakers would probably say that they want to tell a human story amid massive special effects, and that they want things to feel intimate; oh, except every other zombie movie ever has already tried that. What a big-budget project about a global undead attack can and should offer is huge-scale battles and setpieces - when the movie's doing this, it's a lot of fun (I saw it in 2D, so I can't speak to what an extra dimension might add).
If you're looking for armies versus zombies, though - you're not going to like this, but most of that appears to be being saved for a sequel. After scenes of global disaster, the climax of this prospective part one is decidedly small-scale, more like a single player Resident Evil-style survival horror adventure than a massive melee. The annoying family become really fun exactly once - during a night-ops mission with a SEAL team, Gerry's phone rings at just the wrong moment because his wife is giving her daily call to check on him. What husband hasn't been there? Most of us never had flesh-eaters attracted to our every ringtone, but the satirical exaggeration is fun, and what zombie movies should be doing. As are the reasons that the countries who are doing well under siege have managed to survive - North Korea, for example, has all its citizens undergo mandatory dentistry so nobody in the nation can bite anything. With this and Warm Bodies, it's nice to see some Romero-esque satire returning to the form.