Michael Cook, “The Koran: A Very Short Introduction”

This was a very informative book, and the point I found most interesting was that the Muslims accept the proposition that one verse of the Koran can abrogate another part of it (the author likens it to a constitutional amendment).

The book is objective.  It points out some problems with old texts and so forth, but nothing overwhelming is noted.  The authors says that the reason for the uniformity of the texts now is that the state early on made it so:  It picked one version and all the others were destroyed.