If you have seen the 1st and 2nd parts, you'll notice a few matching events between those previous movies and this one. It's another parallel story, not the beginning as you could read from it's title: "Genesis", instead of a genesis, you get a love story that gets caught in the middle of a zombie-possessed infestation.
At some point the shooting style changes from the hand-held camera to director's view, which although refreshing, breaks the sequel style. I think the first two parts were scary, but this one became a mix of action, gore, with a touch of comedy that also breaks the sequel style, specially some illogical behavior under stress situations. Acting was OK, special effects were not disappointing.