I'm not sure it works in a contemporary setting. It was written before CCTVs, madeleine McCann, tight school security and mobile phones and internet. So when a child vanished they were just...gone. There wasn't the online presence to keep them alive. And there wasn't the range of securities we take for granted now.
But also, the book is all about time as a slippery dimension, so you gradually get an impression that Kate has just slipped through time, not been taken by a weirdo. If you try to reduce that to a straightforward plot, you lose almost all the subtlety, so it looks at the end as though, 'Oh good, they're having another baby, so that's all right then,' whereas in the book the ending is unbelievably moving.
I thought the acting was good but the adaptation was ridiculous. It needed to be far more confident that it was different from every thriller going, and show the audience that it was about timeslips, rather than trying to tout itself as The Missing feat. Benedict Cumberbatch.