I havent read the book, but knowing hollywood and its distaste for a storyline, I will assume they just used the title like in I Robot.
The pacing was terrible. It was an okay genre movie but highly immemorable and not worth ten bucks. All of the visual effects worth mentioning were in the trailer. I SOOO didnt see 200million dollars worth of special effects. I assume most of that was due to reshooting the last 40 minutes after the test audiences hated it.
The battle strategy in the last hour "tunnel crawl" was pathetic.
Scientist one: "hey, let's walk through a big tunnel full of killers and get to the very end of the building, since this steel bar is all that stands between us and imminent death"
scientist two: "ya, we are totally trapped in the completely glass filled building surrounded by a town of people completely unaffected by any kind of zombies...you know...so much so that brad pit and a hot boy-girl just walked right up to the front door without any problems whatsovever. trapped I tell you."