Half-Blood Prince is a foray into new territory. It's definitely the darkest of all the Potter movies, but it's still witty, delightful, and full of the kind of magic that makes each HP movie so engaging and pleasurable to watch. It has multiple sides to it, no doubt, and perhaps that's what makes it such a fascinating movie -- and one that will quickly become the favorite of many, many viewers.
You ask for it and Harry Potter and the Half-Blood Prince has it. This movie has its slow, sad moments that make you tear up, and yet the crew has somehow pulled off the feat of making such a depressingly ominous movie shine with happiness and the most comedy Harry Potter has seen yet. This is one of the golden movies out there that makes you laugh and cry within the span of the two-ish hours. (Prince is 2 hrs, 33 min.)
There's no doubt that Half-Blood Prince has its sticky moments. Some scenes require more smoothing, and others are simply not done well. Weasley's Wizard Wheezes isn't given much time in the movie, which is disappointing, but the sixth installment brings out some characters that lots of people (including me) would have never considered "favorites" before this. A few names?
Bellatrix and (Draco) Malfoy are now my absolute favorite characters out of the movies. They're portrayed as "bad guys, stay away" somehow, in the books, which turned me off about these two, but in the movie they're fantastic. The actors are superb, and Bellatrix and Malfoy are brought to life so realistically that you can't help but love them -- Draco for his mysterious aura throughout the movie, and Bellatrix for being so dramatic and just all-around mean. She's very likable.
Harry Potter and the Half-Blood Prince isn't perfect. It's close. It lacks some of the signature fighting that is the trademark of every Harry Potter. But this movie is sheer genius and an absolute treasure to behold. It's out-of-this-world amazing.