My first impression of The Tortilla Curtain was that Boyle was simply wallowing in the smug glow of his PC sensibilities- 'You see I UNDERSTAND these minorities and SYMPATHIZE with their plight. And although I'm probably a rich Californian I live in an ungated community so that the Mexican immigrants are free to enter my street when they come to clean my house and do the yard work.'
However he did create some reasonably believable characters both for the Mexicans and the Californians, though their roles in the story were more than a little typecast. (but then just because it’s a cliche doesn't mean it isn’t true)
His depiction of the gated community itself was amusing in a horror-show fashion, vaguely reminiscent of the Agrestic community in the first series of Weeds.
But in his efforts to be non-partisan and show that both sides have flaws and difficulties nothing seemed to go right for anybody and nobody was happy. Even good people were condemned due to who they were not what they had done. The story became a litany of unremitting misery.
The sweeping finale with wild fires and floods offered such an opportunity for Mother Nature to wreak revenge, leveling the two sides and uniting them, or at least bringing them together, through adversity.
But Boyle seemed unable to exploit the potential of his own magnificent metaphor and allowed the torrent to rage past merely heaping more misery on our protagonists and then abandoning them with no satisfactory conclusion.