Philip Pullman, The Golden Compass  351 pages
The first book of a trilogy, His Dark Materials.
This book begins with one of the most familiar of YA fantasy formulas: Lyra, a stubborn, wild, but brave and intelligent ten year old girl, apparently an orphan, leaves her home at Jordan College (in an alternative world Oxford) with a magic device (the "Golden Compass" of the title, otherwise known as an "alethiometer") and begins a series of improbable adventures (fleeing from a vast, shadowy conspiracy) which soon turn into a quest motif; and it becomes obvious that she is destined to save the world from an inconceivable evil. Add in gypsies, witches, and intelligent animals. How many times have we seen some variant of that in recent fantasy literature? I must admit that I generally avoid this sort of story like the plague.
However, after a somewhat slow beginning, the narrative becomes very fast paced and is obviously better written than most formula fantasies. In the later books, it becomes something else altogether, and this is what justifies considering it more seriously.
Sticking to this book, though, there were some good points and some annoyances. As for the annoyances: It is an alternative world or alternative history novel, which I generally dislike, and despite a science fiction explanation in terms of quantum theory and collapsing probabilities I found it somewhat hard to suspend my disbelief when some aspects of the world obviously diverged a long time before the action and other aspects are so close that they seem to require a shorter time period; there is a combination of advanced and primitive technology which is hard to accept, at times bordering on "steampunk". But this became less bothersome as the book progressed and I became caught up in the story. The second annoyance was with the character of the protagonist; she is obviously intelligent and living in a center of scholarship, yet seems determined not to learn anything from it (this is the same annoyance I have with Harry Potter and most other fantasies aimed at younger people; they all buy into the anti-intellectualism of twentieth century American school life and extend it universally.)
On the positive side, the writing is very good, and the description of the "Church" is very realistically done. However, I probably would not have cared much for the trilogy if it had continued in the formula vein of the first book.
Philip Pullman, The Subtle Knife  288 pages
The second book of His Dark Materials.
The adventures of Lyra continue and the character of Will is introduced. While the book still follows the fantasy quest formula, and continues to be a fast paced adventure, a religious theme based partly on Paradise Lost is introduced, and the trilogy becomes somewhat more serious.
Philip Pullman, The Amber Spyglass  465 pages
The third and final book of His Dark Materials.
In this book, drawing on ideas from Paradise Lost and the New Testament pseudepigrapha, among other things, the story becomes more metaphorical, and the issues involved become more real than the made up threats in other fantasy novels; essentially the conflict is one between free, critical intelligence and uncritical acceptance of authority. While the anti-clerical, and anti-Christian elements come to the fore, the argument is not really focused on religion, it seems to me that rather than using metaphors for God the novel uses God as a metaphor -- significantly, the Church and the angels refer to him as "The Authority". In the end, the rebellion of the angels disappears from view and other aspects of the novel become more important, other metaphors, and particularly "dust", which has played a significant role throughout the trilogy, is explained here.
I enjoyed the trilogy and found it quite thought-provoking, but I think a reader's reaction to it will depend very much on his or her attitudes to "faith" and religion. I can understand why this was challenged by the religious right.
[Spoilers here] On the literal level, the trilogy just doesn't work, because there is a contradiction between the fantasy and the science fiction aspects; the fantasy is based entirely on the uniqueness of the knife, and the final choice of Will and Lyra to not use the knife and to allow all the windows to be closed. But the science fiction explanation for the alternate worlds is a version of quantum theory in which every choice creates an alternative world which only differs from the original at that moment in that the choice was made the other way; so virtually infinitely many worlds would contain knives, each with a different Will and a different Lyra (and other knife bearers) who not only could but must make that choice both ways to create two alternative worlds; so there is no way that all the holes in all the worlds would be closed up. (It doesn't matter if that version of the theory is actually true; it's the version which is presupposed by the novel.) Of course this doesn't affect the metaphorical core of the story.