It is difficult to know exactly what to make of Don Carson's book on the Emergent church - other than that his is profoundly discomforted by them. His analysis seems fairly straightforward. They are good at understanding the times we live in, and to a large extent they accept a post-modern critique of modernity. His main issue seems to be that they are not clear on which bits of modernity they accept and which they reject, nor which bits of post-modernity they accept and which they reject. But given this lack of clarity I don't really see the point of lengthy discussions defending aspects of modernity (that nobody is openly objecting to) nor long discussions attacking aspects of post-modernity (that nobody is explicitly advocating).
When it comes to his more specific critique of some of the writings of Brian McLarren there is a similar concern over Brain McLarren's lack of academic rigour in terms of what is left unsaid, but given that Brian McLarren never claims to be writing for academics the criticism does seem weak and leave the impression of being more pedantic than anything else.
Don Carson appears to be looking for something to criticise, but is finding it difficult to do so, because the Emergent church seems to be refusing to define itself in black and white terms that would enable this. Perhaps that is the heart of the issue he sees with the Emergent church - that there is a worrying lack of rigour that he sees potential dangers in, but, overall, I did not find this a helpful book. Certainly it is less an introduction to the Emergent church than a polemic against.