I don't even know how to begin. Of course, you must KNOW that any film with Benicio del Toro, Naomi Watts, and Sean Penn is going to be good. But the subject matter in this film makes it absolutely necessary to have actors of this caliber play the part of these flawed yet very human characters. It also requires a director with more than just a passing understanding of human relationships.
This movie touched my heart in a way that I don't even fully understand. The story itself takes place in chunks of timelines, much like how you would remember a dream or an event in the distant past.
As I watched these narrative parts become whole, I understood that this movie shows life as it is, not as people imagine it to be. Which seems like it would be easy, but I imagine it's harder to depict reality than it is to elicit fantasy. When you gently but completely pull the curtain back on fantasy, you can more fully see the inner lives of the characters. And with the right story and the right actors, those inner lives are compelling enough to want to carefully keep track of each piece of the story as we come to see it, and to "bond" in a way with each character.
In the U.S., blockbuster films have conditioned the populace to think in terms of "good guys,' "bad guys," "beginning" and "end." This makes it so that many Americans have trouble navigating stories without those crutches to help them along. If you watch this film with a more nuanced, fully human appreciation of what it means to be a mortal being, you will be speechless at the end as well. And your heart will understand the story more than your head.