Anyone who has read Max Brooks's grippingly detailed science fiction novel – or even better, listened to the superb audiobook – will probably have a pretty good idea what kind of movie Brad Pitt originally envisaged when he bought the screen rights to World War Z in 2007. Delivered as a series of oral histories straight from the lips of survivors of the zombie apocalypse, the book presents a steady, nagging creep of horrifying reportage from across the world. It's like a set of zombie-infested episodes from Radio Four's From Our Own Correspondent, or Studs Terkel's vivid and entrancing An Oral History of World War Two rewritten by George A Romero.

One can imagine Steven Soderbergh directing a border-straddling ensemble piece in the style of Traffic or Contagion, with zombies replacing drugs and infection as the dramatic active ingredient. Pitt is said to have initially imagined a zombie apocalypse movie with a genuinely geopolitical flavour. At some point in time, it appears he had one: those who have read Changeling screenwriter JM Straczynski's initial draft of the script, say it had the potential to catapult the genre into awards season territory.

Since 2008, when that screenplay leaked, matters have taken such a turn for the worse that Pitt must surely be starting to regret ever naming his production company Plan B. First Straczynski's script was jettisoned for failing to hit the necessary action tentpole beats, with The Kingdom's Matthew Michael Carnahan brought in to do a complete rewrite. Then, after the shoot finally completed last year, Pitt and his team decided (with the help of Lost's Damon Lindelof) that the entire 40-minute-long third act would need to be reshot and replaced at vast cost. There are also rumours that Pitt and director Marc Forster refused to talk to each other on set by the end of production. As we head inexorably towards the film's 21 June release, some reports suggest the budget has ballooned to more than $400m, which would make World War Z the most expensive film of all time.

So negative has the publicity surrounding Pitt's movie been thus far that the film's producers appear to have just about given up trying to stem the flow of negative hype. A recent Vanity Fair article on the star's "epic struggle" to make World War Z delved extensively into the movie's shortcomings, candidly exposing the collective myopia of a creative team that apparently had little experience of big-budget, spectacle-heavy film-making prior to entering production. (At one point, an entire day of filming was lost because the caterers didn't have enough food to feed 750 extras, and later on producers discovered a cache of undocumented unpaid bills from a Malta shoot that added considerably to budget costs.)

Lindelof reveals he was called in and asked to give his opinion on World War Z's ending, which pretty much everyone involved admitted did not work. "The thing we really need right now is someone who is not burdened by all the history that this thing is inheriting, who can see what we've got and tell us how to get to where we need to get," Pitt apparently told the screenwriter.

Lindelof then gave producers two options: a rewrite of existing material to make it work better in terms of "emotional stakes and plot logic, and all that", or a complete rewrite which would require dumping footage that had already been shot. "I didn't think anyone was going to say, 'Let's throw it out and try something else,'" he admits. But so upset were executives with the previous finale that they agreed to the screenwriter's plan B with little argument.

Brad Pitt in World War Z Photograph: Paramount Pictures

The new version is ironically said to be less spectacular, but with more of the sense of emotional relief supposedly required to send cinemagoers contentedly out into the night. Carnahan's version is said to have seen Pitt travelling to Russia to free legions of slaves, who he enlists to destroy the zombie threat with lobotomising sheaths that take off their heads. But it was too grim and violent for the PG-13 film Paramount insisted on and cast Pitt in a negative light as a savage, zombie-killing warrior leader. Worse still, it failed to reunite our hero with his family (and therefore felt hollow and bleak).

What's apparent here is that somewhere along the way, Pitt simply ended up optioning the wrong novel. Brooks's intelligent alternative history beautifully posits the collective inability of global political administrations to function in the face of an entirely unexpected threat, and the appalling ramifications of their failure on ordinary individuals from soldiers to doctors to priests. It's a satire on the sloth-like clumsiness of even the most sophisticated forms of government that's notable for its lack of a traditional Hollywood-style central figure. The idea that one man could make such a big difference in the face of worldwide meltdown, at least in the traditional action-hero sense, is laughable to anyone who has read it. And yet, in the trailers for World War Z it's apparent that everyone's favourite Chanel No 5 advocate is being hyped up to be the saviour of humanity.

Hollywood used to have a history of making a mess out of supposedly "unfilmable" books, but in recent years it has become apparent that audiences are more than willing to see traditional filmic narrative techniques jettisoned if it means telling the story they have come to know and love. Stories don't always need to be curtailed, simplified and souped up for the big screen, at least not so ham-fistedly that nothing is left of the book's original spirit.

With its elegant documentary-style approach, Brooks's novel reignited the sagging zombie genre in the literary world, so it's incredibly disappointing that the movie adaptation looks unlikely to do the same for its celluloid equivalent. The only consolation might be that if World War Z does go down in flames, Heaven's Gate-style, it could serve as a warning to studios that butchering much-loved material for the sake of popcorn kicks rarely ends in anything but misery for all concerned.