His Dark Materials Boxed set: "Northern Lights", "The Subtle Knife", "The Amber Spyglass" [Box set] (Paperback)

For those readers who have completed the Harry Potter books, and are looking for something of the same kind (as I was when I began reading this trilogy), I'd advise you to drop any pre-conceived notions about how 'young adult' fiction is written - these books have bite. Main characters are subject to questionable morals, the plots are trully labrynthine, the whole Christian notion of the nature of the Universe is picked apart almost in disgust, and characters that you find yourself caring about do die.
To compare this trilogy to Harry Potter (which I enjoyed) is to compare wine to fruit juice.

As the author himself admits, the three books are really all one book, in much the same way as The Lord Of The Rings. I defy anyone to read the first story and not want to immediately start on the second, then the third.
The tale focuses on a girl called Lyra, raised as an orphan, but with a great destiny. Her adventures begin with a struggle against the all-powerful Christian church in her world, which is parallel to our own, but with many subtle differences.
This struggle leads to a greater one, and a greater one, until her final destiny is revealed - one that has implications for all the parallel worlds in the Universe.

Bringing together cosmology, physics, and christian theology, the trilogy presents a unified theory of the Universe, one in which even God himself may not be everything he seems (please be aware from the outset that Christians may find many of the aspects of this Universal theory uncomfortable, but also remember, it's only a story).
Even on a scale as grand as this, you can't help being drawn into the minutae of Lyra's world, her struggles, her emotions, and the realities of her burgeoning adolesence.

Be prepared for an emotional involvement in this trilogy. Whether you agree with it's somewhat grey-area moral stance, you won't fail to be impressed by it.

The books combine fascinating and philosophical (in fact partly theological) plots with truly complex characters and issues of morality. This is not a schoolboy romp in the Harry Potter mould nor even a dark epic quest in the Lord of the Rings mould. If anyone has read Susan Cooper's "Dark is Rising" sequence and liked it, then the feel of the books is perhaps closest to that.

Having read the other reviews I find it hard to understand the complaint that Northern Lights starts slowly. At pretty much the very beginning is an attempted murder and a basic introduction to a new world. Most inquisitive minds will want to know why the attempted murder happened and I found that from the beginning I wanted to know more about the other world.

Fantasy is a genre that many have difficulty with. However, in His Dark Materials all the characters are very human in bearing and thought - even the armoured bears.

I cannot recommend these books as much as they deserve. I hope that in time they will take their well deserved place beside C.S Lewis's Narnia Chronicles and The Lord of the Rings. As a 25 year old I have difficulty in remembering any books that I have found as involving or morally complex.