I taped this due to the recommend in the NYT television section and it was right. I kept getting apprehensive from the moment the backpacker turns up. The suspense of approaching terror reminded me of the growing sense of horror in Chabrol's Le Ceremonie.
Two quibbles: what mother would leave her baby in the bathtub for only a few seconds. And what mother would leave her baby alone on the beach? The mother obviously had a dark side to begin with; she was lonely (trying to reach her husband for several times without success) and was an easy prey to the backpacker. While the ending horrified me, it shouldn't have surprised me. What was great is the movie didn't drag on and was short.
Definitely worth watching and it left me shaken for a long time after-wards. Like Le Ceremonie, it will remain in my memory. Horror doesn't mean slash and gore.