Quality of writing is, to be frank, not why I read these books. Yet I was really taken by the image of a depressed Hermione, sitting on the front desk of an empty classroom, dejectedly conjouring birds that flying around her head in a circle. Goodness, it sounds stupid when I say it like that, but I thought it worked.
Also, it is striking how they use the word "snog" for "kiss" in all sorts of contexts where one might define it as something a little further along if one didn't know what it meant. I guess that's going to fly over the heads of anybody who doesn't get it.
Ps. Told you so.