This was a very, very good movie. It was interesting and well done. However, the film strayed from the book drastically - major events were omitted, yet random scenes completely irrelevant to the rest of the movie were added in (for example, the scene where we first see Harry). Also, the "romantic" side of the story was emphasized A LOT.
If you haven't read the book, this is brilliant. Don't get me wrong, this was very enjoyable...it's just a different telling of Half-Blood Prince. I thought Tom Felton did an especially outstanding job in the movie. Everyone played their parts very well, and it was a pleasure to watch...if sometimes bizarrely different than the original novel.