When I wrote that piece asking where all the 9/11 novels were, a friend wondered to me how a novel about 9/11 could even be possible when we already know all there is to know about what happened. As you say, the last thing we need is another minute-by-minute reconstruction of a day most of us remember all too well. Like you, I admire Jonathan Safran Foer (whose brother Franklin is a colleague of mine at the New Republic) for taking on this challenge. Though Foer doesn't depart from the actual events in any meaningful way, I suspect he will be criticized for daring to fictionalize that day at all. A letter to the New York Times in response to a recent article on this spring's crop of 9/11 novels takes issue with the Beigbeder book you mention, pointing out that the novel's characters couldn't have had breakfast at Windows on the World that morning because the restaurant was occupied by a conference. Clearly, feelings of proprietariness about 9/11 still run strong.
Of course you're right that nobody could call Foer a social realist. But I don't think we should dismiss realism as a possibility for writing about 9/11, especially since the pages of his novel that deal explicitly with it are the book's most realistic—and, I would argue, successful—moments. Oskar learns "what happened" (poignantly, he only ever refers to it indirectly) soon after he arrives at school; he's let out early and arrives home shortly after 10 a.m. to find the phone messages from his father—until then, he says, "I wasn't even a little bit panicky, because both Mom and Dad worked in midtown, and Grandma didn't work, obviously, so everyone I loved was safe." Foer's choice of the messages as a focal point is a particularly good use of realistic detail, because the messages left by people who died in the towers were an especially human part of the 9/11 story, and an aspect of it that I—and I suspect many others—had temporarily forgotten.
The power of these moments reveals an unexpected gift of Foer's: He's capable, at times, of saying nothing, letting emotion express itself through omission. As you've pointed out, this is rare in a novel that's otherwise stuffed to the gills with journal excerpts, letters, typographical tricks, and other antic devices, some more effective than others. I can't condemn Foer's use of magic realism entirely: My favorite part of the book (there's nothing so pedestrian as chapters here) was the fable that Oskar's father tells him as a bedtime story the night of Sept. 10, which imagines that traces remain in Manhattan of a "Sixth Borough," once attached to the city, that has slowly floated away. When the people of New York realize the borough is receding, they use enormous hooks to drag Central Park, the jewel of the Sixth Borough, to its current location. The hole left behind struck me as a moving metaphor for the gaping loss in Manhattan after Sept. 11. (Another point of realism in the novel, as we see in the bedtime-story episode, is the relationship between Oskar and his father, which Foer tenderly and sparingly evokes.)
This novel is obsessed with filling in what is empty: Oskar's father's coffin, the silence at the end between Oskar and his father, the emotional chasms that so many of the characters carry around with them. The trouble, I think, is that some of these things can't be filled, and Foer doesn't always know when to stop trying. You compared Oskar, in his precocious intelligence, to Ludo in Helen DeWitt's remarkable, underappreciated The Last Samurai, but like some other reviewers, I'm afraid I found him fairly charmless. He doesn't seem to feel the suffering of others so much as compute it: He is fascinated by facts—one of his favorite expressions is " ... which I know about"—and he seems to believe, or at least to hope, that accumulating them will help compensate for his loss. But the result is often too much information. It's understandable that Oskar can't always separate what's important from what's not—after all, he's only 9. But his creator needs to be able to, and this novel doesn't convince me that he can.
If Foer's brand of imaginative realism is to work, it needs to be grounded in, well, reality. In one sense this is not a problem for the novel: It doesn't have to prove to us that 9/11 occurred, after all. (Talk about a convincing impossibility!) But, if it means to adhere to novelistic conventions at least to some extent (and I think Foer, for all his innovation, does), then it must offer us a main character who is, if not necessarily a reliable narrator, then reliably unreliable. Like Alex, the gibberish-spouting Ukrainian translator in Everything Is Illuminated, Oskar struck me as too deliberately idiosyncratic to be credible. Is believability too pedestrian a criterion to apply to such an inventive and playful book? Where should we draw the line between imagination and falsity?