This is a good movie... if you haven't read any of the books. While visually, the effects were great, they were about ALL that carried the movie. In fact, there was very little of the original storyline from the book.
There were key plot elements from the book missing. In the book, there were a number of memories Dumbledore put into the pensieve regarding the origins of Tom Riddle (Voldemort) that showed where he came from, underlying what the horcruxes were, how he got Slytherin's ring (he killed his Muggle father and made his uncle Morphin Gaunt take the blame), etc. They left out Bill Weasley and Fleur Delacour's engagement and Molly Weasely's dislike of Fleur. They left out the DA's involvement and their taking the rest of Harry's Felix Felicis potion, the involvement of the Order of the Pheonix, Bill getting injured and Fleur's acceptance of him even though Fenrir Greyback had disfigured him, leading to Molly Weasely's acceptance of her. They got Tonks all wrong. At first, in the book, when Harry arrives at the Burrow, she is crying on Molly's shoulder, and it is only later that we find she has been in love with Lupin. In an added scene, during the movie, at (supposedly) Christmas break, she and Lupin are already together. The actress who plays Tonks is not the same Tonks, neither in style nor manner. The Death Eater attack in the movie that resulted in the burning down of the Weaselys' home was NOT in the book, and was graphic and grossly unnecessary.
As well as Fleur and Bill, Rufus Scrimgeour is completely left out, and it is not even mentioned that he became Minister of Magic. Percy Weasley is not present. All house elves are left out. Moaning Myrtle is not present, and she is a major character in this book. In the book, she mentions to Harry about the "boy crying in the bathroom" (Draco Malfoy), and when he and Harry have the battle in the bathroom and he is near death, it is she who cries out "MURDER!", alerting people of what happened. In the movie, she is absent, and Professor Snape's unbidden arrival after Draco and Harry's "scuffle" makes no sense at all. The parts of Bellatrix Lestrange and Luna Lovegood were beefed up, and while I enjoy both characters and the actresses who play them to perfection, such an addition did not sit well with me. Also, in the book, Dumbledore was killed in his office with Harry under his invisibility cloak, unable to move, speak, or react. In the movie, he was killed somewhere else. Wrong, wrong, wrong.
I did, however, enjoy the Weasely twins' shop. They got that right, at least. I laughed watching Hagrid and Slughorn absolutely plastered together after Aragog's funeral. Draco Malfoy was perfect. No longer the spoiled brat he once was in the other books/movies, he is shown in his own coming of age. His father in prison, he is desperate to prove himself, although the task, murder, is daunting. He cries in the bathroom and uses round-about ways to do it because, deep down, he is not a killer, which, until death, Dumbledore sees. The teenage soap operas revolving around Hermione and Ron, as well as Harry and Ginny, are well done, reminding us that this is not just about good and evil, magic and wonder, but about teenagers growing up and coping with homework and romance. Alan Rickman, as always, is perfect as Professor Snape. You can see as he makes the unbreakable vow, the look on his face that highlights his lack of willingness, yet lack of choice in the matter. You can see his division as he struggles to protect Harry, as well as to protect Draco Malfoy from spiraling down a dark path from which there is no return. He very aptly portrays Snape's reluctance to kill Dumbledore as he must, both as the unbreakable vow dictates and as Dumbledore asks.
In short, plot-wise, they got more wrong than right, making the movie a gaunt version of the full richness of Rowling's original novel. The visual effects alone, while wonderful, were not enough to feed the movie's anorexic plot line.
While I did not exit the theater within the first hour, as many of my fellow movie-goers in the theater did, I left the movie theater disappointed, outraged, and cheated. I felt I had wasted precious time and hard-earned money. This movie is not worthy to carry the book's title "Harry Potter and the Half-Blood Prince", but should be dubbed "Harry Potter and a half-assed attempt at a movie".