So what's so good about The Mars Room? A pathway into the novel's profoundest insight can be found in its ending, which I initially rejected as a failed attempt at epiphany that collapses into the hoariest Romantic nature cliches. Further consideration, however, led me to revise this opinion. The ending's nature epiphany and Romy's ambiguous capture (or killing) actually succeed as an encapsulation of the Kunderan "secret the novel asks about" (quoting from my favorite passage in The Unbearable Lightness of Being). Kushner's deepest theme is something we might call "the prison in the garden": the transformation of America, in its citizens' imaginations, from a land of Romantic promise to a carceral state. No, that ending isn't flawed at all; it's Kushner's ticket to the Great American Novel sweepstakes, her book's major statement about the way we live now.
Another plus is Kushner's prose. Like much well-reviewed contemporary litfic, The Mars Room impresses me most at the level of sentence, paragraph, voice. Kushner arc welds some marvelous metaphors, ably ventriloquizes a diverse set of characters, and can orchestrate a paragraph of free, indirect narration into a soliloquy that ironically reveals a character's ultimately fatal narcissism. (I'm thinking specifically of the long paragraph on pages 304-305 of the hardcover, in which Kurt Kennedy thinks around his visit to Cancun and his obsession with Romy/Vanessa.)
But even with these important positives, the book still feels rather 'thin,' a minor novel trying desperately to be major. Given that I had the same thought about Jesmyn Ward's two recent National Book Award winners, this probably points to a larger problem in our culture--about which, see the parenthetical last paragraph of my post on Jesmyn Ward, below.