The interactions between Harry and Ginny in this chapter are very solid; it shows just how much they've grown to be comfortable with each other.
Ginny's outburst during the conversation with Dumbledore shows how much she's come to know about him.
I love the twins; I always have. They're good creations and fill a void left by Fred and George. They also give a good foil to the trio.
Two thoughts: the first is that I'm not sure Hermione should have been able to cast her Reductor Curse, as it is over the holidays, but being at Hogwarts might have changed that.
Second? I hate any 'had had' constructions.
This is a good chapter. It shows Harry growing into being a leader and how well he's established trust with people - and how Dumbledore is trying to re-establish trust with him.
I especially like Ron's reaction to Voldemort's name, Instead of just being the name of the Dark Lord, it's a more personal fear.
You bastard! You killed Hedwig!
I've wanted to write that for years. Honestly, I'd forgotten you'd killed her. Powerful chapter.
You never did address why Ginny was crying at the beginning of the chapter thought.