Okay. Here's the thing. While I am openly and happily a fan of the Harry Potter novels - there goes my street cred right out the window, but hey, I read the first one in a single sitting and that's got to count for something - I've never been particularly bothered by the films. I saw the first three out of some sense of moral duty but my interest just sort of petered out after that and I have yet to see entries four and five. I realize that this means that I willingly paid money to see the Chris Columbus version of Harry Potter while declining to see the Alfonso Cuaron version of Harry Potter which is, admittedly, a very curious thing to do, but the films just... well... they just lacked something.
Looking back on them now, I can see that the first two films suffered largely from being a bit slavish to the text, and not particularly imaginatively so. Columbus obviously didn't want to stray too far from the source, but just couldn't duplicate the charm of Rowling's text, so they suffered from the direct comparisons. And number three? Well, three is where the books start getting too long to be contained by any sort of faithful film adaptation -- but the third film made the mistake of trying anyway, an approach that failed both versions because there was no room to jam everything in without making it feel awfully squishy while also making the bits that were omitted stand out all that much more.
Harry Potter And The Half Blood Prince? Of the Potter I've seen on screen this is the first time that the film felt like its own entity, separate from the book. And that is a good thing indeed. Beyond the tired - but true - argument that film is its own medium with its own demands, the simple fact is that if Half Blood Prince were adapted one hundred percent faithfully you'd probably need a miniseries to contain it all. There's a lot in there. Director David Yates goes an entirely different road, paring things back to their essentials and creating a story that works cinematically rather than trying to make the audience feel like they're watching a book.
Hardcore fans will, no doubt, slam Yates for his omissions. And there are lots of them. Hagrid is reduced to a cameo. The only teacher to actually get any in-class time on screen is Jim Broadbent's Professor Slughorn. Of Harry's classmates outside of the inner trio only Neville appears at all and then only in one scene. Even Voldemort is completely, one hundred percent absent. If you weren't told that Harry was in school you'd have precious few indications to let you know that he was, and there is virtually nothing shown of Harry and his friends simply being kids between classes and adventures - the area where most of Rowling's unique charms really come into play on the page. So don't go expecting the book.
But, as a film, you get something better than the book. You get a relatively lean action-adventure with Harry beginning to come into his own. Half Blood Prince is where Harry really begins to come of age. And by that I don't just mean the boy-girl pairing off that takes place throughout - the repeated instances of Harry's classmates hidden in the background making out are rather amusing once you start noticing them - but this is the point in the saga where Harry really starts to take control of his own life and destiny, accepting what he is, what role he has to play, and what the consequences could mean to himself and those close to him. Part of the particular genius of Rowling's saga is segmenting Harry's life into distinct years and watching as he grows and changes from one to the other - starting as a child, going through adolescence, and grappling with adulthood - and this is where that final stage begins.
Though I don't find the peril put on screen quite perilous enough - and never as emotionally charged as it is on the page - they've done a solid job with the material here. Jim Broadbent is his customary stellar self and the core trio continue to put in solid work. My money is that Rupert Grint will be the only one of the core trio to have a significant career once Potter is done, but the group works well together.
I often lament the death of the 1980's kids adventure movie, films like The Goonies and Monster Squad. Potter's not that - he's too big and safely corporate in his film incarnations to match the quirky, unique energy of those old films - but, for the time being, he's the best we've got by a healthy margin.