One quick thing I love about it, the cover...I saw the DVD from the right side and I see Malfoy and Snape. Odd I thought, but cool. So I picked it up and from the left side, it looks like Harry and Dumbledore. I know it's trivial but its the little things I try to smile about.
If you've read the book you probably spent a good majority of the movie going "where did that scene go?" and yes there is a lot missing. The Half-Blood prince was simply too dense of a book to fit into a 2 hour movie. A lot of the book is building up to what happens and unfolds in the final book, I would have rather seen this film in two parts then leave out scenes (or add scenes like they did). I think for this movie to be fully enjoyed and understood, you would definitely need to read the book.
Spoilers Ahead (actually if you read the book these aren't spoilers, just things you might have noticed are missing): These are just some of the more important scenes that are left out: The final Hogwarts battle, Dumbledore's funeral, Sirius' property being stolen, Harry and Ginny's relationship and its ending, where are the older Weasley boys?. There are other parts that are gone, other reviewers have already touched on them.
I did give this movie four stars because I feel it did deserve it. One star because its a Harry Potter film, I enjoy the series. Another star for the chemistry between everyone. It was great, especially now since they are coming of age, hormones are running wild and love is blossoming, its a normal part of growing up. It also provided a great balance to the darkness that overtook the movie. Another star for the emotional conflict of Malfoy, it was excellent. He was able to get more screen time and we see his internal battle. And the last star for, the acting. I think everyone did a great job portraying the emotion or lack there of in the film. Except the ending, I felt more emotional reading the book than what came across on the screen. After a slight let down of this movie, now the wait begins for Nov 2010 for part 1 of the Deathly Hallows (or maybe not since it's the same director).