I'd class this more as a zombie novel that might appeal to those who don't usually read zombie novels. I found the whole intelligent zombie angle refreshing, but I agree that it lost much of its sparkle after they left the compound. Probably because that's when it started to more closely resemble traditional zombie novels.
We must have been reading this book around the same time... I just finished it too. :) It looks like we had similar reactions. I also thought it got tedious once it turned into a string of zombie chases.