Short review: I think the first part is really good. I really wanted him to talk more about cultural issues of transmission of the gospel. But he seemed to be a bit convoluted toward the end of the book. This is somewhat dated with references to Christianity in public schools and issues with communism. I want to read more by Newbigin to see if he is clearer in other places.
My full review is on my blog at http://bookwi.se/foolishness/