The canon of the zombie genre is not set in stone, but it generally follows that George Romero’s films are the authority from which all subsequent variations derive. Not being based in fact, those variations are many. For instance, we all know that in order to kill a zombie, one must destroy the brain. That is, unless the film in question is Return of the Living Dead (a film that prides itself on being zombie apocrypha, as it were), where nothing short of total incineration can kill a zombie. Or 28 Days Later and it’s sequel, where the zombies (not zombies, according to the filmmakers) are not undead but still living, and can thus be killed by anything that’s lethal to a normal person. Or The Last Man on Earth, from before the genre had a rulebook, where a stake through the heart was used to dispatch the hordes.
Romero and John Russo’s Night of the Living Dead established that the unburied dead come to life and hunger for the flesh of the living. What about the buried dead? Presumably, if they haven’t rotted away, they are thrashing around in their coffins, trying in vain to crawl their way to the surface. That restriction was lifted in Return of the Living Dead (which Russo had a hand in). In that film, coffins, concrete sarcophagi, six feet of dirt and pronounced decomposition are no barrier to the undead. They rise from the ground below and hunger not just for the flesh of men, but for their brains. The not zombies of 28 Days Later aren’t interested in a meal, just inflicting grievous injuries to any poor soul that happens upon them.
Zombies can’t talk. Unless, once again, the film is Return of the Living Dead, The Last Man on Earth, or the obscure yet compelling Deathdream, where the undead are fully capable of having conversations with the living.
The causes of a zombie apocalypse vary so much that there is no cause that fits within an established rule. The main culprit is usually mankind itself, filmmakers never seeming to pass over the opportunity to comment on the ills of society. Such as in Return of the Living Dead, where the zombies result from corpses being exposed to toxic chemicals. In 28 Days Later, a weaponized virus was the cause, an origin picked up by the direct to video remake of Romero’s Day of the Dead. 
The loose ethics of a supercorporation and it’s own virus research played hell with mankind in the Resident Evil series of movies. In C.H.U.D., which hovers on the edge of being a zombie movie, the grotesque deformities of the monsters are the result of homeless tunnel dwellers being exposed to radioactive waste. In The Last Man on Earth, the zombies are infected with a viral form of vampirism, while in another interpretation of the source material, The Omega Man, there aren’t any zombies at all, just a small remaining percentage of mankind that has taken on a bleak complexion that complements their newly misanthropic temperaments.
In Dead Alive, or Braindead, depending on the country, the zombies are set loose by the bite of an exotic jungle rat-monkey, the progeny of plague rats that had their way with Sumatra’s indigenous population of monkeys.
In Lifeforce, vampirism comes into play again, but with an otherworldy origin, as the initiators of the zombie plague are sexy aliens from outer space. Night of the Creeps also had aliens play a role, as they developed and then released leech-like creatures onto the earth that infest and then breed inside humans, turning them into zombies à la the Cordyceps fungus or Toxoplasma gondii. In Maximum Overdrive, a film that removed humans from the role of the undead and replaced them with semi-trucks, the cause was either an alien invasion or the tail of a comet (Stephen King, writer and director, couldn’t seem to make up his mind on this).
A séance could inadvertently raise the dead, bringing the supernatural into play, as is the case in Children Shouldn’t Play With Dead Things. Or, as in Deathdream, the prayers of a mother for the safe return of her son, away at war, prove to have dire consequences.
In some films, when a person dies, they immediately turn into a zombie. In others, a person can die and not turn into a zombie as long as they were not bitten by a zombie. At one time, zombies were slow and lumbering, shuffling their way towards their victims. The trend of late is to have a person’s agility and speed remain intact even after turning into one of the bad guys.
An accounting of the variations of the zombie genre can go on and on. The above is just a sampling of what filmmakers have to work with when they tackle the genre. Even in remakes, such as 2004’s Dawn of the Dead, there is always enough wiggle room to keep things fresh.
The original Dawn of the Dead followed a group of survivors on the day of the zombie apocalypse as they found refuge in a shopping mall. The remake, directed by Zack Snyder, follows this theme. A police officer, Kenneth (Ving Rhames), a nurse, Ana (Sarah Polley), and the mysteriously bland Michael (Jake Weber), are among the survivors of the environs surrounding Milwaukee, a city that is being eaten alive so quickly that there is little time to react.
The mall seems a great place to hide, and it becomes an impregnable fortress for the small cast to wait out their days under the comforting glare of fluorescent lights and the soothing drone of muzak. Of course, any normal life can be that boring, and that’s not what we go to movies for. So the filmmakers thrust the survivors into increasingly more hostile situations as the film progresses.
Compared to horror films of the past, and the original Dawn of the Dead, the remake conducts itself in a serious manner. There is little lightheartedness throughout the film, and the gore, while outlandish, is designed to be more realistic than cartoonish. The characters are caught in a desperate and bleak situation, and the filmmakers use this to create tension. Mostly, this newer, serious treatment of the source material works. In real life, one could imagine that there would be a fair amount of weight were one to survive the end of civilization.
Dawn of the Dead was not a film that needed to be remade. Since it was, however, it is good that the film establishes its own atmosphere and its own world early on. The zombie plague is frightening and well handled. The film effectively invests the viewer in the plight of the survivors (Should they wait out the rest of their days in the mall, or venture out to try and find more permanent safety?), leading to a denouement that, while not unpredictable, still keeps the audience guessing which of the characters will survive to the next day.
This new Dawn of the Dead is straightforward and conventional when it comes to being a zombie film. The zombies are of the fast and agile variety that has become the norm of late, but other than that, the film fits in nicely with past zombie fare. Why it succeeds as another entry in the genre is it chose strong source material to draw from, it is simple in all the right places, it has no reek of cheapness, and there was enough care evident in making the film that it is unlikely Snyder and the rest could have come away with anything less than a decent film.