Movies in 15 minutes - Harry Potter: HBP recap is up at cleolinda's blog. If you didn't see the movie and want to know what happens, or if you did see the movie and want relive it again and again, or if you are bored and want to kill 15 minutes, I recommend reading it.
I've seen the movie twice, and there are a couple of things I'd change. I'm not going to write a list of how the book was different/better than the movie OMG, because I get that movies based on books are going to be different. Unless it's Watchmen, where the only difference is the addition of awkward sexy porno music.
The most egregious difference between the movie and book was probably the "1933- The Great Depression blah blah blah bankrobbers blah blah John Dillinger" text at the beginning and then the scene where Johnny Depp gets out of a car and shoots up a prison. But then the movie theater people realized they were playing Public Enemies and switched it back to Harry Potter. Not fast enough to anger a theater full of angry Mormon families whose children were no longer pure, having been exposed to 3 whole minutes of an R-rated movie. How crude.
The most annoying actual difference between the movie and the book, in my opinion, was the blah-ification of Ginny Weasley. She's awesome in the books. She's hilarious, smart, pretty, loyal, protective, and you totally get why Harry would like her. I am grateful that we never heard anything about that stupid "chest monster," but I didn't need to see superfluous shoe-tying scenes.
The only other difference that bugged me was replacing the electric Snape/Harry confrontation after Dumbledore's death with a night-time hiking trip through the woods that ends up getting a little tense. There was supposed to be shouting! Unforgivable curse attempts! Snape totally losing it after being called a coward! But nope. It's: "Oh btw I'm the half-blood prince, bbl!" I read somewhere that JK Rowling originally wanted Tim Roth to play Snape, and I think I would have liked him better. I think Alan Rickman totally looks like Snape, but I think his performance is always a little subdued. He's supposed to be this intense, angry, desperate, remorseful man and Alan Rickman's Snape seems so disinterested and tired.
Even with those complaints, I really liked this movie. It's the only Harry Potter I wanted to see in the theater more than once. The look of the movie is gorgeous and the three main kids have a lot of good interaction. Easily my favorite out of the entire film series so far.