The book doesn't quite suffer from being boring because now all the initial action happened in the first book, but events must be set up for the third book so nothing happens here. However, it does seem like Lyra was dumbed down because she makes some decisions that I don't think she would have made. I never understood why she actually bothers to get in the car with Sir Charles, who randomly spoke to her at the museum. Yes, I get it she was running from the “police” and may have thought she wanted to get away but she wasn't that trusting of people in The Golden Compass. That's another thing; there are two guys specifically after Will and the letters from his father, and then they just kind of vanish after they almost catch Lyra at Oxford. It seems like they were working for Mrs. Coulter or Sir Charles, so I would have expected to see them show up in one of the other worlds. Also how does Mrs. Coulter suddenly have such a command of the specters that she can make them do things that they never did before? They did not take to the air until “she made them forget they were bound to the earth” and now they can conveniently attack the witches? That seems to be lazy way of creating a new problem for characters who didn't have to face the a problem before.
Pullman also seems to like killing characters once their “task” is done, and it feels a bit unnecessary. Scoresby leads Grumman to a mountain to meet with the knife bearer, now let's kill him. Grumman meets Will and helps him, oops, time to die now. At least the death of Sir Charles actually fits the plot and most of the character motivations.
Here's hoping the third book is better.