Grenz and Olson write from a sympathetic, yet critical standpoint. Their main analysis is over the transcendance/immanence tension throughout the history of Christian Philosophy. The 20th century theologians are a reaction to the classical liberalism of the 19th century, but in my opinion, they do not go far enough. The theologians they survey that I enjoy the most are Karl Barth, Karl Rahner and Wolfhart Pannenberg. The ones I dislike the most are Jurgen Moltmann, Paul Tillich and Hans Kung.
I also enjoyed reading about Narrative Theology, too, because I think some of it is similar to Reformed Biblical Theology (see Geerhardus Vos, Herman Ridderbos or Richard Gaffin for an example). Reformed Biblical Theology places its emphasis on the outwork of the Redemptive and the Christotelic nature of scripture, much as Narrative Theology places its emphasis on the developing story or narrative of scripture.
The big issue I have with 20th century theology is its doctrine of God. The big theological move is more toward a panentheism, rather than the distinct creator/creature distinction. They see God's transcendance/immanence in temporal rather than spatial categories. This has led to the questioning and denial of the Immutability, Impassibility and Foreknowledge of God. The logical conclusion, in my mind, is process theology, which holds that God is Di-Polar. His pole of being is finite but his pole of becomming is infinite.
My biggest problem with the book itself is that the authors are very open to this possiblity, but personally I am not, and see it as nothing but Hegelianism. Other than this caveat, however, it was a good introduction to the subject and I would recommend it to anyone studying the theological landscape of the 20th Century.
The book begins with an illuminating discussion of the Enlightenment and the problems it threw up for theology. The birth of comtemporary theology is then charted through the work of Schleiermacher in the nineteenth century, to a tried and trusted (?) canon of modern figures, ranging from dogmaticians such as Barth and Tillich, through liberation and feminist theologians, to more 'post-modern' types in the section on Narrative Theology. Very comprehensive for a relatively slim volume. I was engrossed throughout, and my passion for modern theology was kindled by this excellent book.
Of course, any book such as this has to be selective in its material, and some major figures are either ommited or glossed over. There is a considerable Protestant bias with only two Catholic theologians being considered (Rahner and Kung) and not a word about Eastern Orthodox theology, which is becoming a fashionable study in theological circles. By way of other Catholics, both Von Balthasar and Schillebeecks would have been worthy of inclusion. I also feel that a chapter specifically discussing the phenomena of so-called Post-liberal theology would be helpful: in particular the work of George Lindbeck, which has been revolutionary over the last twenty years.
In terms of style, my only criticisms would be that there are occassions when more explanation would be desirable, and that Grenz and Olson's criticisms can (albeit rarely) become a little pedantic. All in all a highly recommended, dare I say enjoyable, read.