I came to this book after the twist was widely known, so I knew from the beginning that Alice Blackwell is a fictionalized Laura Bush. I think that the process of coming to realize that this is the case would have been electrifying, and I'm sorry I couldn't read this book without prior knowledge, but I do feel the book stands strong even with its secret revealed.
Sittenfeld's Laura Bush is fascinating. She has liberal values, but no passion about them. She has class consciousness, but she unquestioningly forgives the extremely privileged people in her life for not trying to understand their effect on less privileged people. She has morals, but doesn't really make her decisions based on them. She's passive, private, almost quiescent. Her decisions seem to be based on her emotional reactions to past events, rather than on a strong moral character. And, being married to a politically controversial and even divisive person, her own moral positions on political issues is constantly questioned by the public -- but Sittenfeld gives us a Laura Bush who is motivated by completely different issues, and who lacks both the channels and the inclination to explain her inner self to the public.
One thing this novel exceeds at is explaining how an unremarkable, slightly liberal school librarian could be charmed, then swept off her feet, then wed by George Bush. In fact, as others have pointed out, this novel may be more successful in explaining George Bush to us than it is at explaining Laura. Sittenfeld's descriptions of him ring absolutely true.
In the final section of the book, the public harm done by the Bush administration forces Sittenfeld's Laura Bush to examine her own culpability, which focuses all the experiences she has in the first part of the book into this one question. Although I found several preceding parts to be a bit slow, the book really picked up for me as this moral question came into focus. Many readers were dissatisfied with Alice's conclusions, but I felt there were consistent with her character, and every compromise she had made, and I thought the novel as a whole was successful. Recommended.