Extra Virgin Olive Oil. What's so great about it?

I see a lot of praise for extra virgin olive oil, especially for its health benefits. They say it's high in polyphenols, which do wonders. But I'm not quite sure why it's better than regular oil. Is it really that important for your health, or is it just marketing?

So how do you choose an oil that's truly extra virgin, and not just one with a pretty label?