Ok, this is possibly my favourite film of all time. Lars Von Trier is at his best working under the guidelines of the Dogme 95 manifesto, if you're familiar with Dogme you'll know what I'm on about, if not, it's best to read it up somewhere else, it basically concerns back-to-basics 'pure' film-making. I had to study this film on my Film Studies degree course and was blown away by it. BEWARE though, if you don't speak Danish and you don't get on well with subtitles, because throughout the film there are points when they are pretty tricky to read due to the fact they are white and sometimes on a bleached out bright/light background. THAT though is my only complaint with the film. The story is highly original and thought-provoking. The characters 'spaz' ie act as though they are mentally ill, as a social experiment. Sometimes 'spazzing' in the local community - at swimming pools, or cafes, other times doing it in their secluded house. It can be very sad one moment and extremely funny the next. Things inevitably get a bit carried away and what started as a group of friends having some fun disintegrates into tears and depression. If you're even considering getting a copy, just do it. I can't recommend it enough, and there's no way I'm spoiling it for you by telling you what happens :-)
PS Watch out for the sex scene if that kind of thing bothers you. It's not exactly subtle.