It wasn't about ONE guy fighting a horde of zombies like this movie seem to be turning into.
Did I say "one guy"? No, I said "epic". You can't tell me that parts of the book weren't epic like the battle of Yonkers or the retaking of the U.S. Yes, as a posted previous to you, they have basically put aside what the book was about.
I think it would have been very easy to do the movie in the style of the book. You could just frame each story with Brad interviewing the narrator of each story. Heck, they could have gone pretty cool with it and had different directors with different styles for each segment. But NOoooo, Brad had to be the Hero with a capital "H" and cause a total rewrite of the concept of the book. As typical with Hollywood, they licensed the book but threw out everything but the title.