Firstly,lets get this straightened out, they are not zombies. I don't know why they used this title, I believe the US title is Wicked Little Things, which is far more fitting.
Now, misleading titles and cannabalistic gore aside (both if which are there just to compliment each other and don't really have a place in this film), this is actually quite a nice little ghost story for bedtime. If you can forgive the zombie faux pas, you will see that this film posesses all the nice qualities of a traditional bedtime ghost story. The plot is rather good, the visuals aren't bombarded with melodramatic music, it is quiet and gentle, with evil ghosts that you can sympathize with. It has the typical nightime scenes in the woods, old houses, old newspaper cuttings that tell the story of the children who worked in the mines. All these things are used well,and not overdone.
The gore is a bit too much, it is too obviously an attempt to gross you out, which is not needed. Personally, I feel that horror films have become so obsessed with being as gorey as possible, that cinema is really missing some good old fashioned ghost stories, this is one that I think is judged too harshly, okay, so it's not as good as the Orphanage, but it is worth watching.