Okay, a little more detailed than that. J.K. Rowling's writing style has definitely matured along with her characters and her audience. While her main characters are instantly recognizable in their habits and actions, they are also very obviously teenagers now. Harry spends most of the book in a snit (ah, how I remember being fifteen!), and Hermoine and Ron are also moodier and more prone to anger and lashing out.
All the old favorites make a return, and some who were intriuging in the past are elaborated on further (such as Snape, Neville, Sirius, and Cho Chang, Harry's crush and the late Cedric's girlfriend). Some other new characters are particularly interesting, and the new Defense against the Dark Arts Professor is a real monster. I think we've all had teachers or known people like her, and I'm sure we were all glad when they were out of our lives. The Weasely family also has a very prominent part in the new book, and since I think the Weasely's rock, that made me very happy.
Yeah, I really enjoyed it. #3 remains my favorite in the whole series, but #5 definitely gave it a run for its money.
*****Slight spoiler alert: I'm going to be as oblique as possible here, but don't read this part if you haven't read the book and want to be totally surprised.*****
Three moments in #5 that absolutely broke my heart:
--when Mrs. Weasely battles a boggart.
--when Neville's mother gives him a Christmas present.
--when Harry tries to get in touch with Sirius using a mirror.