Then again, I'm typically slow to see fault and quick to forgive...
Those are wonderful qualities to have. Hang onto them with both hands.

Here's my take on the character inconsistencies:
I certainly don't feel that they shouldn't be maturing (which they are), but to me it seemed their basic characteristics in this book were strangely off. Harry hardly thought of Sirius more than once, Hermione didn't seem to be looking things up half as much as usual, none of the kids seemed to really care about Hagrid beyond the obligation they felt to him... When you take into account that only a few weeks had passed between OotP and HBP, it's rather shocking that their behaviors and feelings should have shifted so much and with little or no warning.
On the opposite end of the spectrum, you have Draco Malfoy. We've had hints of what we'd find, but until this book we never saw how much he really loves his mother, and how scared he can be under that viscious veneer. I thought we got to see changes in his character, but done in a really gradual and insightful way.