Nagel isn't actually as unreasonable as I feared; in particular, he realizes that conceivability arguments are largely pointless unless one is an expert on the thing being conceived: it proves nothing, for example, that I can imagine my having a headache without my brain being in any particular 'brain state'. I can also imagine a group's per-capita income going up even while every single member of the group becomes poorer: I'm imagining it right now, with a little green arrow pointing upward labeled "average income", and a bunch of stick figures with frowny faces standing around as cartoon coins jump out of their pockets. Does this prove that it's not a contradiction in terms, merely a coincidence that it's never happened?
Still, Nagel writes off a lot of possibilities kind of fast. He says that the 'objective view' can never be complete, because no matter how many 'steps back' you take, the fact that you are holding your NEW even-more-objective view of the world in your mind is a fact about the world that your description of the world doesn't take into account. (Why not? If a theory needs to explicitly enumerate every true fact about the world to be complete, then nobody can ever actually understand a container of yogurt, let alone the entire universe. And if it doesn't, then any theory which purports to cover the existence of human minds at all could clearly subsume an incident of human-understanding-the-universe that had not yet occurred at the time the theory was formulated.)
He's much more lucid on ethics (and morality, etc.), which takes up about half the book, but not much is there which can't also be found in the denser The Possibility Of Altruism or the less abstract Equality And Partiality, both of which I recommend more highly. This was interesting, as Nagel always is, but I don't think I got much from it beyond a few moments of fear that I might not actually be human since I don't share the anti-materialist convictions that some philosophers consider to be the necessary result of introspection by any non-robot.