it was a pretty loyal adaption, with elisions rather than alterations (the bear duel and the rescue were swapped in order being the biggest i noticed). with a large-cast book this means you get lots of minor walkon parts with no depth. not sure this is a good thing.
i think they tried to fit too much story into a 2-hour film. the bears were particularly ill-served with the stuff about bears only being trickable if they are behaving like humans excised completely (hence ragnar/iofur's downall and iorek's shame), and i don't think gandalf made a good iorek. i did not much like the way the alethiometer was handled, either, with it apparently presenting visions rather than Lyra working to figure its language out.
i like the bit at the end where Lyra notes that they are "bringing him what he needs". oh indeed you are, Lyra.
this book could withstand this treatment. but i do not want to see a version of The Subtle Knife made like this.