Want to waste an 1h 46m of your life? Because, this is a great way to do it.
Nothing happens for 99% of the movie. Seriously, the YouTube channel, "CinemaSins," couldn't sin this movie. As for the few things that do happen, it's all predictable. Including the ending.
It's gross, more than scary, and you almost never see the zombies.
One theory is spit out about what could stop the zombies, but they never actually delve into it. We do get a, "why?" At least.