^Um, the book was a pretty "epic zombie war". Did you read it?
It was and it wasn't. Tone and context makes a huge difference and the tone of the book wasn't some grand sweeping epic about a global zombie apocalypse, it was a collection of very personal stories set against the background
of said global zombie apocalypse. Filming it as just a straight-up zombie flick rather misses the point.
They appear to be just making a zombie film in the style of a Roland Emmerich disaster movie when what they should be emulating is something more along the lines of 'Crash' or 'Babel'.