This is an extremely well structured masterpiece by Lars Von Trier; if you like original and inventive storytelling (the entire movie is set on a stage with VERY few props, there is even an invisible dog) then I strongly recommend this film to you. On the other hand, even if dramas aren't usually your thing I would still say that the chances of you receiving the film's strong message(s) are high.
The story begins when a woman called Grace (Nicole Kidman, obviously) appears in a small town one night after we hear two gun shots being fired. A young man (Paul Bettany) welcomes her to the town and the pair immediately agree that she should work for the town's residents in return for their welcoming arms. All is well at first, but during the course of the last two hours terrible things begin to happen and by the end Grace is forced to face her inner monster, with drastic consequences for the town.
What unnerves the most, despite her horrific encounters with members of the town, is the fact that when she resorts to shockingly extreme measures, the viewer simply cannot help but side with her, sympathise, even secretly cheer her on.
It is on that note that I let you decide on whether or not you rent/buy this wonderful, riveting piece of art; bearing in mind that it's effect on you could be overpowering.