OK, I've now seen it twice. I'm allowed to form an opinion. And it's kinda freaking me out that I am about to pan a Harry Potter movie.
Harry Potter and the Half-Blood Prince was good in all technical respects but it was so dark, both in mood and photography I just couldn't get into it. I also never got over what they left out. Sure, the novel is 652 pages, so a ton of stuff had to be omitted, but in Goblet of Fire and Order of the Phoenix, it didn't bother me so much. Then there's the gray, gray everywhere, almost like it was a black and white movie. Sure, it's a dark novel but there is still so much magic in Harry's life, both literally and figuratively, that this gray palated, dour mood movie just sucked all the fun out of it.