Rating: WORTHY!
This is another Harry Potter novel that opens with no Harry Potter in sight to begin with. This is also the novel which Rowling herself felt best about in the entire series from what I've read: the one which she liked the most, and which she spent a lot more time in planning, having learned a lesson from the difficulties she had with volume four, which necessitated an extensive rewrite. I think this is conversely, my least favorite!
This time we get Bellatrix Lestrange, arguably the most powerful witch in the entire seven volume series (aside from Molly Weasley, of course!), and her kid sister Narcissa Malfoy apparating to a location close to where Severus Snape lives in a rather run-down neighborhood. Why they don't apparate somewhat closer to his house than they do is slightly mysterious, but I guess you can explain that away by their desire to remain unobserved by Muggles, but this begs the question as to why they would even care.
It's a rather bigger mystery as to why Wormtail is staying with Snape. Draco Malfoy has evidently been tasked by Voldemort with working on a cabinet hidden away in the Room of requirement. This cabinet has a twin in the Borgin and Burkes dark magic shop off Diagon Alley, which Harry encountered in Chamber of Secrets - another example of Rowling's intensive long-range planning of her seven book series. Death Eaters plan on using this to get into Hogwarts. Why? Seriously, why? We never learn.
The ostensible plan is to murder Dumbledore, but they could have done that at any time. Throughout their entire novel, Dumbledore is traveling, it would not have been hard for the death eaters to track him down and "do him", but once again we're locked into Rowling's one-year plan, so to kill him off earlier would have failed her scheme of things, but this still fails to explain why Dumbledore was considered so far advanced beyond any other wizard in his power that he was the only threat to Voldemort. I find it hard to credit that out all the witches and wizards on the planet, there was quite literally no other wizard even approaching Dumbledore in power, and who was also a good person. It beggars belief.
Evidently Draco is now a Death-Eater and getting others into Hogwarts, and killing Dumbledore, is how he will prove himself. Why get Death-Eaters in if Draco is going to kill Dumbledore? They did nothing when they arrived so what was the point? The main problem is two-fold here, from what I can see. First of all, why Draco? Snape is already there. He could let Death-Eaters in any time he wanted. If they absolutely have to use the cabinet, he could have fixed it and presumably far faster than Draco did. So why Draco? I have no idea except that once again we're writing to formula instead of to a realistic plot pace and authenticity, and so we have the adventure play out over an entire school year and employ one of Harry's rivals rather than an adult.
The second issue is: why would anyone actually want to join Voldemort? They're wizards. They can do and have anything they want, quite literally, so where is the impetus to subjugate themselves to a psychotic wizard? Voldemort's motivation is criminal, but at least he has one. He wants to dominate the Muggles, kill-off the "half-breeds" and rule the rest, but to what end? He's no better off then than he is as a plain, ordinary wizard, and he has the added headache of all that responsibility! It makes no sense, but then Voldemort didn't have to.
Voldemort doesn't need a goal since he's completely loony tunes, but you would think others do. I mean there would no doubt be other psychos who would join him because like attracts like, but this fails to explain why so many people would actually volunteer for his crusade. What would it net them that they don't have already? It's the same problem with some of the James Bond stories. Why would criminal "masterminds" spend billions to set up something which would only serve at best to recoup the billions they've had to spend? None of it makes any sense!
Harry appears when Dumbledore once again uses him in much the same way, since we've already made the comparison, that 'M' employs James Bond: as a blunt instrument to achieve his ends, but at least Bond gets the facts; Harry never does! In this case, the job is to recruit Horace Slughorn as potions master, yet we never learn why Dumbledore was so obsessed with hiring Slughorn. Yes, Slughorn had this knowledge about what Voldemort was up to way back when, but Dumbledore could just as readily have got that by doing some magic on him and reading his mind. This elaborate farce was nonsensical.
The bigger question is why didn't Dumbledore, who himself dabbled in the dark arts when he was younger, already know about horcruxes? It beggars belief to think he would be ignorant, given his history and his relationship with Tom Riddle. Besides at this point, Dumbledore already knows that Voldemort has made horcruxes. So we have this whole story built around retrieving information from a character which ultimately tells us nothing that we didn't know already. The most crucial piece of information was how many horcruxes Voldemort had made. This was the key to defeating him since every one of them evidently has to be destroyed, but Slughorn did not have that knowledge. The simple use of a time-turner would have been ideal for tracking Voldemort's actions, and identifying the horcruxes and their secret locations, yet never once is this put forward as a solution! Plot hole!
It's a bit obvious from the start that the potions book which Harry gets hold of belonged to Snape and that, therefore, he had to be the Half-Blood Prince, and who cares anyway? It's not like unraveling this "mystery" actually solved any dark problem or brought any evil-doers to book. I think this is why I disliked this book perhaps more than even Goblet of Fire (although the two are close!). It really wasn't a story like the others were, it was more like six hundred pages of exposition. And Rowling got away with it!
And what about the staff shuffle? Suddenly, Snape is now absolutely fine as the teacher of the Defense Against the Dark Arts class? Why now after sixteen years is it perfectly fine to give him the job he's most qualified for, but not at any time prior to this? Again, Rowling offers absolutely no explanation whatsoever for this. Plot hole!
Why Hermione gets so angry with Harry is a bit of a mystery, too. Yes, she has a valid concern about his use of the half Blood Prince's potion-preparing tips, but to get so bent out of shape is overkill. It's a school text book, not a dark arts book, and the tips work. Besides, how come she didn't simply come up with a spell to show who used that book over the years? She was always magically on top of things at other times, why not now? She does pull out a spell to test it for dark influences, but she never thinks about tracing its history? Again Hermione is made to look dumb.
Harry's newfound 'facility' with potions does help win him the bottle of Felix Felicis, and it's cool how he tricks Ron into thinking he got lucky in quidditch, but the fact that Harry's sudden excellence in potions trips no one's alarm bell is a complete mystery. Wouldn't McGonagle have wondered, even vaguely, how a poor student - which is, let's face it, what Harry was at best - could have risen to brilliance over the course of one summer with no practice? Once again wizards and witches are shown to be amazingly blind and stupid. And what's with Harry's "acceptable" being unacceptable for pursuing a higher education? The scoring system makes no sense!
In this volume, Dumbledore suddenly has time for Harry, but he still won't tell him what's really going on. Once again, Dumbledore is shown to be a complete a jerk - and a moron, too. So his hand is cursed - so what? Cut it off and have Madam Pomfrey regrow it healthily. This is never put forward as an option, not even to shoot it down with some magical explanation. It's merely left hanging there which again makes wizards and witches look clueless and inept and Rowling look like a bad writer. And if this is a deadly spell, why isn't it included along with the other unforgivable curses?!
We do get to see some interesting history and enjoy the pensieve once again, which I always thought was cool in the movies, although if they were a person's memory, it was completely ridiculous that we never saw the imagery from that person's PoV. This is a mistake made frequently when exploring memory, but it's really, really bad in Rowling's case. If it was person X's memory, then that memory would never show person X from a third person perspective. And what's with the idiotic Muggle clothing - the guy wears a one piece swimsuit under an overcoat? Where did he even get that idea? This merely serves to highlight how profoundly stupid and moronic the wizards and witches are in Rowling's world. It's not even funny.
We learn, during the course of these visits, that there are at least three horcruxes, two of which are already destroyed. The first was down to Harry stabbing Tom Riddle's diary with a basilisk fang in Chamber of Secrets and the second was Dumbledore's sole contribution to bringing down Voldemort. He destroyed the locket at the cost of his own life - or more accurately at the cost of his own pointless death, but he never once explains to Harry how to destroy the horcruxes, verifying yet again what a swine Dumbledore truly was. None of this tells them how many more horcruxes Voldemort has created or where they are - so how does Dumbeldore know that four remain? (There are actually five, but once again he's lying to Harry about that because he's a manipulative a jerk).
It's in this volume that Ron and Hermione finally hook up, although what she sees in him is a complete mystery. Harry also gets it on with Ginny, who's had the hots for him since volume one, according to Ron, but none of this really goes anywhere or contributes anything to this story.
Dumbledore shows what a weak wizard he is by being utterly unable to figure any way around the potion guarding the locket. He couldn't get an inferi to drink it? He couldn't magically line his alimentary canal to prevent harm, and drink it himself? Clearly Voldemort here has defeated the supposed most powerful wizard in the world. This is the price of Rowling's determination to weaken and kill off Dumbledore, but it makes him look stupid again. He has to be killed off at any price, so there you go.
One thing I never did get at the end was why the movie people changed Rowling's original story. In the book, Dumbledore freezes Harry (who is hidden under his invisibility cloak) and he literally cannot do a thing, yet the movie has him hiding one floor below the top of the tower, where he could have helped, but failed to do so. In short, the movie made Harry look like a coward and a loser, which is completely adrift from how the book had portrayed him. Go figure! I don't get why Rowling allowed them to get away with such an abusive change to her story.
This is how Harry gets to see Draco disarming Dumbledore, and thereby unknowingly taking possession of the Elder wand, before Snape comes up and carries out Dumbledore's instruction to kill him. It's also here that Harry proves himself once again to be a self-centered jerk when he abandons Ginny, who is fighting for her life, in his blind-rage pursuit of Snape. He could have donned his invisibility cloak and taken down several of the Death-Eaters, but he fled the scene, ignored the needs of his supposed friends and the Order of the Phoenix members, and ran away. Jerk.
Harry also shows how weak of a wizard he is - and this is the year after he has been teaching "defense against the dark arts" to students - as he fails to get Snape, but this isn't even the most inexplicable thing here! We have Death-Eaters in the castle, and they have a chance to wreak havoc, yet instead of firing Avada Kadavra killing curses, destroying everything in sight, and perhaps unleashing fiend fire into the school, they're using pathetic high-school level jinxes? Clearly Rowling didn't want to kill off scores of her reader's favorite characters here, but this is a massive plot hole, every bit as big as the one in Order of the Phoenix, where they previously failed to kill anyone.
These are supposed to be death eaters - feared and deadly, dangerous and remorseless, yet every time we encounter them, all they ever do is vomit up weak as weasel-piss amateur magic. Where the hell did they ever get their reputation?! I consider this a major failing on Rowling's part. I can see how she wouldn't want this kind of thing in the very earliest volumes, but these kids are now fifteen, sixteen, seventeen, and yet she still offers us no more danger than she did in volume one!
So the story ends with an unnecessarily dead Dumbledore, and HRH vowing to destroy Voldemort by eradicating all his horcruxes. This, for me, was the most boring book in the series maybe in competition with Goblet, yet it still got a story told and kept my interest in following the series.