His Dark Materials is a trilogy in the true sense of the word - the books cannot be read out of context or out of sequence. There is no time lapse between the three volumes and very little mention is made of previous circumstances once the story has progressed - the reader is fully expected to be clued in to what is going on at every stage of the complex story. As the author himself says in a small introduction at the beginning of each book, this is a story in three books, not three books which are connected by a common theme. This is not exactly a revolution, but nevertheless a welcome departure from the current marketing driven trend of writing series into which a reader can enter at any time in order to maximise sales.
The single biggest upheaval of fantasy laws achieved by Pullman is his approach to good and evil. Not a single character is completely on either "side", because, despite the claims and protestations of some of the powers involved in the conflict at teh center of the story, that is not the line which divides the two camps (in itself a major departure from fairytale lore). The readers are not expected to place their sympathies with one coalition or with another, and any ideas which are formed in the course of reading are constantly undermined and re-examined. The protagonists are neither aware themselves, nor are shown to the reader to be clearly on a particular side, and it is only at the end of the book that one can retroactively decide (and even then, in a somewhat tentative manner) who was in the right and who was in the wrong ( and even then people who may have fought on the "right" side were bad people who did wrong things and vice versa).
Pullman weaves a complex net of personal loyalties, prejudices, interests and affection into sets of alliances which in are infintely more powerful in helping the actors in the book claim allegiance to side of good than any moralistic or self righteous predestinations. Put more simply, no single character int he books is "good" or "evil" - evil is as evil does, and often right is achieved through the most selfish and roundabout of motives. This moral complexity is in itself enough to entrance and captivate a reader whose imagination has been stunted by the clear cut, almost despotic portrayals of good an evil in literature and other media. Even the most urbane adult reader can be cought up in these tangled relativistic webs.
There is also present in the books a wonderfully unselfconcious attitude towards the sexes, an area which has often been criticized as the genre's most backward feature. Witches are mostly female, and gerat warriors are mostly male, that is true; but the crux of the issue is that neither are more important or powerful than the other, and neither sex is being presented as more of a plot mover in any sense. In fact it would be impossible to predict whether any of the characters are going to be male or female just from reading a synopsis of their roles. Alongside this fluid approach to sex there is an equally uncomplicated view of species, or even cosmic states - ghosts and angels, bears and tiny people are all both good and bad, clever and silly, important or marginal. Real and unforced pluralism at its best, and very contemporary in a way that perhaps only the currently growing up generation of readers can fully appreciate.
While predestination and fate are central to the plot, this does not carry with it a fatalistic approach to characterisation. The most visible aspect of that is that although most of the people in the series communicate in English, they nevertheless speak in slight dialects - there is not such a confusion of languages that any one language becomes solidified, no such profusion of worlds that any world is a uniform, single nationality, humanoid reflection of the next. Some of the different universes in the book are similar to our own to such a degree as to be surrealistically confusing, others are so far removed that only a leap of faith can allow them to exist.
Stylistically as well as narratively, this work is miles removed from the impoverished mundanity of contemporary children's literature. There is harldy any direct exposition in the book. From the outset the reader is plunged directly into a world where things are just what they are, however different they might be to the reader's everyday reality. Physical and cultural phenomena which are similar to our own are called by different names, used in different ways, and are never explained or excused - the reader is expected to either figure it out for themselves or fill in the gaps as best they can. This respect for the reader's imagination and intelligence goes a long way towards making this book a work of real fantasy, in the proper sense of the word, rather than some kind of moralistic allegory behind a thin veil of improbable or imaginary worlds.
Another possible demand from the reader is that of general knowledge. The book makes use and mention (although occasionally in roundabout ways) of everything from Catholic Dogma to quantum physics and beyond. While not being aware of the context behind those references will not stand in the way of enjoying or understanding the story, it is nevertheless entertaining to notice and understand them, and hopefully might make children who don't understand ask questions and try and find out about such things as Christianity, the theory of multiple universes, the difference between gas lighting and electricity, zeppelins, and why polar bears don't eat penguins.
All in all this is the best children's book I have read in years, maybe ever. Best not in the sense of being most entertaining, most ethically correct or most inclined to get children to read, but in the true sense of being a damn good book which does not patronise its audience or pretend to be anything but a great yarn, yet still manages to be infinitely more than just that.