Most of the characters, no I think all of them, are sharply drawn caricatures of either hypocritical wealthy redneck pseudo-liberals living in a gated California enclave, or poor hapless powerless victimised illegal Mexicans (how many adjectives can one sentence hold before it explodes?). Toss in some menacing rich white bully teens, mix with evil Mexican canyon denizens, add in a few natural-and/or-manmade disasters occurring at always exactly the wrong moment, and there's your story.
These characters are, for the most part, intensely unlikeable. The few likeable characters are irritating because you keep thinking, "Move on! Move away!". But they aren't listening to the voices in my head.
The characters were stereotypes, and it felt like Boyle was flicking switches calculated to trigger specific emotional responses. 'ok, moral outrage here, sentimental sympathy in 3,2,1, now!'
But it sure does get you thinking about the plight of Mexican illegals, and the limitless cruelties so easily perpetrated by so many, without guilt or self-awareness.