This book is caught between two places: whilst still retaining its standing as an acclaimed piece of academic philosophy, it also tries to make itself readable to the general public. In this it seems quite successful - the topics are interesting and well engaged with, with interesting examples and some unusual arguments that everyone with an interest in philosophy will appreciate.
Unfortunately, the major problem is that Nagel's arguments and conclusions are not always made explicit. This is the kind of boom you can read and think that you have understood perfectly, and yet if try and draw his arguments out in to basic premiss and conclusion form an utter nightmare ensues. Nagel leaps about, tackling objections before he's finished proposing something, switching to discussions of rival theories without any warning, failing to make the link between premises and conclusion explicit and occasionally embedding his actual conclusion somewhere near the beginning of the argument, without restating it.
The problem that ensues is whilst it seems prima facia simplistic to follow his dialogue, analyzing his arguments becomes a nightmare. And that, I think, is the major problem. It seems to me that no one other than the academic or the extreme enthusiast will have the time to sit down, draw out his exact arguments and think about their merit.
I would still recommend the book, but only alongside the warning that you can not expect to be able to engage with his arguments as easily you might have expected to when you first picked it up.