This kind of discussion around von Trier has been pretty typical among movie critics. Can't remember all the details, but typically it revolves around how unsettling his movies are (often from a moral perspective) and whether his vision of the world is accurate. He's not an easy watch; you have to be made of stern stuff to immerse yourself in his vision.
There's definitely a sense of 'going to the bottom of life'... like relentless onwardness, wastefulness. The idea that every living thing in the end gets a losing deal, pain wins out over happiness, bad always outweighs good, etc.
For me, it's like the scientific concept of entropy. You get less than you put in, the universe always takes more than it gives, etc.
There's a quote from Arthur Schopenhauer:
"A quick test of the assertion that enjoyment outweighs pain in this world, or that they are at any rate balanced, would be to compare the feelings of an animal engaged in eating another with those of the animal being eaten."
To which all you can say is-
LOL
Some people could be offended, but for me it was hilarious to read that, because it's such a blunt expression of something I'd kind of always felt.
The movie gets at that in a more heinous, dramatized way.
what the hell is wrong with you people! 
