Half Blood Prince doesn't make me think of Dickens. There's a falling back into the comfort zone. It's like Chamber of Secrets on steroids.
Lots of back story. This is more Voldemort's book than Harry's. We're marking time. It's a transitional work, preparing us for what we all hope will be the whizz-bang climax of the Deathly Hallows.
Of course Harry had to fall in love sometime. I wish Rowling cared more about this side of things. I wish, actually, that she was more interested in her female characters. The ones who come alive are the eccentrics- Hermione, Luna, Tonks. She wants us to care about Ginny Weasley and we're eager to oblige- but do we? I'm afraid I don't.
Slughorn is the best new character. I've known teachers like him.
Boarding schools run on sexual energy. All those adolescents. All that celibacy. I wish there could be more than hints of this in the books, but yes- I know, I know- not in front of the children.
The last hundred pages are riveting. But I don't see how I can discuss them without spoilers.