I finished HP 6 just a few moments ago. It is, well, good but not as gripping as 2 or as epic as 5. It does have a plethora of memorable lines--although perhaps I only feel that way because I'm in the "cult."
At the risk of tipping the plot to those of you who haven't started or finished yet, I have to say that I am inclined to view this year's Dark Arts teacher as a tragic figure, rather than an outright villain.
I thought that JKR handled the teen romance muddles pretty well, although I couldn't help but see a bit of projection of the author herself in Harry's putative girlfriend.
The scene where Dumbledore confronts Malfoy was surprisingly effective, although I couldn't help thinking of the cemetary scene from the Sound of Music crossed with a dash of Jedi.