In some ways, ridiculously implausible (the ability to fine-tune control of memory via pharmaceuticals); in others, mind-bendingly enchanting (U-2200) I liked the first half of the book much better than the second, mostly b/c I liked reading about Marie more than Adam (and the concepts were more novel, and the Us more varied). Also, it's a really tough story to wrap up, and I think he (they?) did a pretty good job of it. I was not disappointed