One of the riskiest ventures Hollywood could sen to venture into is the adaptation of a novel or book into a cinematic rendition. Typically, this leavens the risk associated with an original screenplay, in as much as it provides some measure of the studio's likely return. Books that are adapted have already created a buzz around the author and the work; name recognition and publicity has largely already begun, including what one can assume is a loyal fan base.
One of the risks the studio then faces is the adaptation itself. There is no real way for them to copy the material of a 300+ page book into 120 minutes or so of screen time. This necessitates certain cuts and revisions that could make it or break it with the book's fan base. There are clear examples where the cinematic edition makes it, fully satisfying the books fan base. In the past ten years, we've seen an increasing trend of these adaptations, to varying degrees of success. A recent spate of book adaptations seems to demonstrate this trend is here to stay, and in some cases getting relied upon more and more as a business model.
Successful examples include the wildly popular Peter Jackson Lord of the Rings trilogy, and to a lesser degree the Hobbit trilogy's first two releases, Hunger Games, the Harry Potter series, The Princess Bride, and a plethora of comic book movies but most specifically those tied into the Avengers franchise and their individual spin-offs. These movies gave their audiences something they could buy into and appreciate.
Other successful examples follow a different path. They use the book as a launching point, which can clearly distance a certain portion of the audience. They can easily be sympathized with, expecting a certain thing and given an entirely different experience. Offhand the most successful example I can come up with was Bladerunner, based off the Philip K. Dick work Do Androids Dream of Electric Sheep?
World War Z, the cinematic version, falls mostly into this category. The book, which I reviewed in this post, was a fantastically well done collection of short blurbs describing the zombie apocalypse and humanity's eventual weathering of the storm and rise from the ashes. The movie goes a different path, following Gerry Lane's (played by Brad Pitt) efforts to find the solution to the zombie infestation. The movie itself is largely zombie war porn, with lots of explosions, action and teeth biting into flesh. From this perspective, it largely follows every other trope within the zombie genre, whereas the book's approach was much more refreshing. The movie itself was entirely centred around Brad Pitt, with very little other character involvement or impact, with the notable exception of Segan, the Israeli Defence soldier that gets swept up with Lane's exploits.
I actually enjoyed the experience enough, though I must admit I caught it on Netflix and didn't invest my money and time to go to the theatre; that might have jaded my review. I can't help but imagine how this might have turned out if the studio had thought to provide a movie experience closer to the book. From my prospective, I can only imagine how that would have added to the already cluttered and generic mob of zombie movies that are out there. Something fresh and original would have gone a long way to expanding the genre's boundaries.
I suppose this is simply a reflection of the risk aversion studios have when approving movies for investment. A zombie flick that gives the audiences what they expect is likely a going to reflect a decent return of investment. Throw them something a little more highbrow and they risk facing a loss of millions, regardless of Brad Pitt's tag to the work. I must admit that is likely the fear of all authors and prospective authors dreaming their works onto the big screen (myself included).
The written work is a huge investment of an author's time and effort. To see it adapted (whether by active design from the author or by a studio's direction) into something else may or may not work. The risk, of course, may be too much for the author, and there are certainly enough examples of horrendous adaptations: Starship Troopers, based on the Robert A. Heinlein book of the same name immediately comes to mind. The book was a controversial best seller with political undertones that certainly alienated a number of readers. That said, the work was a solid piece of science fiction, whereas the cinematic version was a campy sci-fi action movie with little depth and wooden acting. I can't think of a movie that did it's book worse justice.
As adaptations go, World War Z certainly isn't the worst on the list, yet it certainly doesn't do much to try and claw up and above the norm expected from its genre. For a movie of this genre, it certainly provides a well produced and enjoyable enough experience. I gave the written work 9/10. The movie gets a solid 7/10 from me.