Aside from the darkness -- which I don't mind ... I'm just surprised -- the movie also didn't quite have the Ron/Harry/Hermione camaraderie that I enjoyed in the previous movies. Mostly, Harry was just going it on his own in the big wizard contest. That was interesting, but it didn't have the multi-character focus. There were multiple characters, sure, but most of them were characterized only superficially (like the other wizard contestants). There wasn't the depth of characterization (of Hermione and Ron, especially) that the series had in previous films. Hermione and Ron felt like minor characters.
I thought the introduction of a romantic element (for all three of the main characters) was nice, given their ages. I wasn't sure how the movies were going to handle the fact that the kids are growing up, that Hermione is getting breasts, that the Weasley twins are incredibly tall now, etc. Shannon assures me that the books follow a similar timeline to the movies, so it's appropriate that the kids are turning into full-blown teenagers.
Some things confused me, probably because I haven't read any of the books. For example, I thought Fleur was killed by the hedges, but I guess not, since she was shown happily leaving the school at the end. I also don't understand how Ron, Hermione, and the other sacrificial lambs stayed alive underwater for so long before Harry et al. saved them. I guess the professors have more powerful magic than the students (well duh) and put them in some kind of suspended animation or something. They looked comatose. But they were still underwater a long time after they "woke up," while Harry was saving them. Confusion.
Anyway, so I enjoyed the movie quite a bit. The special effects were seamless and spectacular, and I had a good time, though I didn't like it nearly so well as the previous movie, because I *loved* that one.