I have to say that I thought this book was ridiculously good. There were some flow problems here and there, but other than that I thought it was great from beginning to end. I think the main reason is that though Phillip Pullman probably did consider a possibly different ending to this book. I am glad he stuck with the one he wrote.
Spoilers for those who have not read The Golden Compass and The Subtle Knife below.
The events taking place are right after readers and Will realize that Lyra has been taken by her mother Mrs. Coulter.
Will who is still in Cittagazze is assisted by two angels named Balthamos and Baruch who try to force him to go and take the knife to Lord Asriel. Yeah somehow Lord Asriel is on the side of good in this book (not bloody likely in my opinion). Will refuses and insists that the angels help him to figure out where Lyra has been taken in order to rescue her from Mrs. Coulter.
Lyra we find unconscious and drugged by Mrs. Coulter. Lyra is having a dream and in it is now talking to her deceased friend Roger (yeah the boy that Lord Asriel murdered in The Golden Compass) and she slowly starts to realize she's hovering in the land of the dead with him. Mrs. Coulter is acting out of character by appearing to be concerned about Lyra.
We also have Doctor Mary Malone who has arrived into Cittagazze and starts to talk to entities known as mulfea.
The characters of Will and Lyra are wonderful throughout. They are each other's best friend. And just like many best friends before them find that they are actually in love with each other. It was very sweet to see them starting to see each other not as a boy or a girl, but actually as a young man and young woman.
We also get some insight into Mrs. Coulter and Lord Asriel though I wish we had not had much to do with them. I think Phillp Pullman thinks that these two redeemed themselves in some way, but I really don't think they did. Mrs. Coulter murdered countless people/children and Lord Asriel murdered Roger. And in Lord Asriels' case, he stayed cold and distant and didn't really give a crap about anyone that was being used to further his own agenda.
I can honestly say that I wish that the stuff with Doctor Malone had been cut or drastically shortened because all of the asides to her threw off the flow of the whole book. Other than when we transitioned to Doctor Malone, every part of the book worked for me.
We had Phillip Pullman incorporating parts of Greek mythology into this book which I was a bit surprised by, but I think if you are going to base book one on parts of Dante's Inferno it would make sense to include more Greek myth into this final book.
The settings of the different worlds were once again done quite well. We had more explanations about the subtle knife, how it works, what Spectres were/are and "Dust". We also have a lot more insight into angels and who the "Creator" was/is and how the different worlds work.
I can say honestly that the ending of this book gutted me. I read and re-read a few times just to have it sink into my head. I don't think it's too soon to show readers that life is sometimes unfair. And even when you are doing the right thing you still may not get your happy ending.