I'm sure I've ranted about HBP before but the problem, as a book-first fan, I have is that of all the movies, it follows its book the least. I know Rowling has last say in the end, but I felt she let that one deviate to far from the book.
Like when
Spoiler the Weasley house is burned in the movie. I felt they were just adding anyhting for dramatic effect, regardless of what it was.
The first two were way too by-the-book, and when translated to screen they came across as somewhat boring. For book-to-movies to be successful, they need to take levels of artistic freedom not present in written stories sometimes. The burning down of the Weasley's house was important to keep the audience engaged. They toned down the climix, so they really had to do whatever they could to keep the movie from just being boring. I'm pretty sure it was the least eventful of all the books as far as overall plot goes. I could really care less about Harry's lengthy investigation of who the Half-Blood Prince is, just get to the Horcrux finding and Dubledore slaying, please.
On a related note, http://www.youtube.com/watch?v=qxZqpV3croQ&feature=player_detailpage