It's really good!
I first read it ~10 years ago and really enjoyed it - and then the movie of the first book came out and that was merely OK - but then I saw an advertisement a few months ago for The Book of Dust which I immediately bought but decided that I should reread the original 3 as I didn't really remember all the details. I refinished them a few days ago.
I read that the first book (The Golden Compass) was actually titled The Northern Lights originally in the UK. Considering the other two books are named after objects/artifacts (The Subtle Knife and The Amber Spyglass) I think The Golden Compass is the better title since it's another such artifact of significance.
I know this was meant to be a story for tweens / young adults and I sure wish I could have read this when I was that age! It's not written in a way that makes it seem like a kids book, and he sure doesn't hold back with some concepts that are probably pretty challenging for a child - but the sorts of challenges that should be made. I'm talking of course of how religion is represented throughout the books... this is fiction taking place (mostly) in another universe, but some of the concepts that are central to the plot almost definitely got some kids questioning what they learned in church and from their parents about the nature of the universe, god, heaven, etc.
There really isn't too much that I didn't like about this series, but I'll try to dig up a few things...
The concept of "dust" is pretty central to the story, and what it is evolves and is teased at all throughout - but I found myself at the end saying "ok, that's it?". I dunno, maybe this was where the nature of the series as children's books caught up to me.
After the first book, Asriel becomes entirely too powerful and influential. He doesn't attain any new powers or at all transform really - he just suddenly is in charge of everything. It's not that he was ever weak - but yeah, the speed with which he goes from being a cunning guy with some resources to being one of the most powerful beings in the cosmos is a bit hard to miss.
Once again, really good! I definitely recommend it to anyone that enjoys light fantasy and that won't be offended by some questions against christianity. If you might be offended by some questions against christianity, then I definitely recommend it - this probably won't make you an atheist, but it'll probably do you some good.
This gets a solid 4/5 stars.