The 12 Most Intense Movies of the 21st Century

What exactly makes a movie “intense?” Is it the way you can’t stop talking about it for weeks and weeks after you’ve seen it? The way you’ll think about it extensively every once in a while, regardless of whether you liked it or not? Is it the feeling of being so enmeshed in the plot you’re watching that you forget the existence of anything else? Is it the way your pulse speeds up, or the way you can’t help but gasp out loud at the right moment? Or is it something entirely different, something you can’t quite place your finger on?