I have not read the book, so perhaps my opinion comes right out of my ignorant ass, but i was pleasantly surprised by the movie. I only heard the backlash on the internet and thought it would be terrible.
I really like that the protagonist is not the super ex military, seal, special forces, bla, bla mega soldier.
And that is, i believe, the biggest problem for most viewers. He was a guy that talked more then used his gun. He worked for the EU/UN and not the CIA/Seal, bla, bla, super soldier producing maschine.
Also the ending was not clear cut. The vaccine was just a temporary solution. It's like the ending from Mass Effect: If it not a super happy ending, todays viewers complain.
Of course the movie was not perfect, it was far from it. But to be honest, i think it was one of the better zombie movies of the recent years. It stands (in my opinion) far ahead of 28 Days later.