He certainly wasn't the innocent 11 year old we remember from Harry Potter and the Philosopher's Stone, pure enough of heart to only want the Stone to keep it from Voldemort, with no thought of using it for himself.
Nor was he the timid Harry we watched in Chamber of Secrets when most of the school avoided him, thinking he was the heir of Slytherin and the one responsible for opening the Chamber and unleashing a monster on the school. We saw Harry grow into a young boy who was brave enough to save his best friend's sister, even though his chance of survival wasn't particularly good.
HBP Harry was not the Harry we watched in Prisoner of Azkaban--the one who learned a powerful bit of magic that he could use to protect himself against the dementors; he was powerful enough to produce a patronus that drove away hundreds of dementors, saving Sirius, Hermione, and himself. Yet, there was still an earnest innocence about Harry in his third year. Unassuming, putting others first, willing to hear out Professor Lupin and Sirius, when they gave every appearance of being the bad guys. Harry was fair and just, granting a reprieve to Pettigrew, even after he learned that it was Pettigrew who was responsible for Harry's parents' deaths. No rash decisions.
Goblet of Fire Harry was growing up. He had more confidence, as he should, by the time he entered the maze at book's end. Harry had been through a lot--again accused of cheating, of breaking the rules to get his name in the Goblet of Fire. But through it all, we saw Harry putting others first--sharing information with Cedric, helping all the hostages in the second task, helping the others in the Maze when he could, willing to share the prize with Cedric, caring enough to bring back Cedric's body. In the end, we saw a Harry who confronted Voldemort in a way he would never have done three years previously.
Then we had Order of the Phoenix Harry, who was angry at everyone most of the time for everything. Many people didn't like this Harry. I wouldn't say that I liked him, but I did think it was about time he got there. Even teens who don't have any tragedy in their family get to the point of feeling that "It's not fair. Why me? No one understands me. My life is so much harder than anyone's else's." And so we spent the 5th book seeing that Harry wasn't nearly as happy as we all wanted him to be. And why should he be? Parents killed when he was a baby, learning that he should have died along with them; robbed of any sort of normal childhood or life as he's persued by a murderous lunatic. I doubt that most adults would be able to keep a cheery disposition, let alone a teenager who was only 15.
To top that off, this is the book where everything that identifies Harry as Harry is stripped away from him--quidditch, the vision of his father as a wonderful person, questioning the relationship between his parents before they married, his new-found godfather Sirius--the first person who could offer him hope of living away from the Dursleys. All of it was taken from him. Then after Harry was tricked by Voldemort, he led his friends nearly to their deaths, as well as his own. What can possibly make things worse? Harry learns of the Prophecy from Dumbledore--and that Dumbledore could have shared that information with him the first time Harry asked when he was eleven. So even his trust in Dumbledore wavers; his image of Dumbledore being perfect is tarnished. But at the end of the book, we start to see a stronger Harry emerge as he heads home for another summer with the Dursleys--not happy, but resolved in what he must do.
That brings us to Harry as we found him in Half-Blood Prince. He has a certain air of confidence that he didn't have before. That's a nice change. He's determined to defeat Voldemort, as Dumbledore walks him down memory lane to see the transformation of Tom Riddle to Lord Voldemort.
Harry is only one year from coming of age, in the wizarding world. He's learning to think for himself, he confides only in trusted friends and his mentor, Dumbledore. But there is something in HBP that we haven't seen before in Harry--a darker side. He's not always choosing to do the right thing. And much of it centers around the used Potion book that he gets from Professor Slughorn, the current Potions teacher.
This is something that we've recently been discussing at HogwartsProfessor.com. While I agree with some that Harry's use of the book is cheating, and with some that using the book was more of a way to move the plot along, I found that I was somewhat undecided about Harry and the Prince's Potion book.
I agree with Mary that Harry's use of the book essentially was cheating. Harry was doing work and presenting it as his own when it was not--maybe lying would be a better way to describe it. If he'd been honest about where he got the ideas, he might still have been able to brew the potions, but he never gave proper credit to the inventor--and that wasn't fair of Harry. And I think what aggravates many people is that Harry got away with his dishonesty--until the very end.
However, along with Sluggy reminding us that Lily was brilliant at potions and our own realization that the Prince was also a brilliant Potions student, we found, in the end, several other things--and I think this may have been the main reason for Harry using Severus's Potions book:
When Harry and Severus weren't spending all their time hating one another:
1. Harry was able to learn quite well from Snape's instructions, even though he'd convinced himself that he couldn't learn anything from Snape--part of the problem with Harry learning Occlumency in OotP.
2. Snape was able to give instructions that were precise and informative enough to be followed, without having to demonstrate them.
3. Without Snape badgering Harry in Potions class, Harry was able to do quite well--even though he was following different directions than those in the official book.
(Is that, in and of itself, really such a bad thing? Education is not just teaching students to repeat what's been done over and over, but is supposed to help them explore and learn from more than one source. Choices again.)
And where does that leave us? Well, it left me thinking that it's not an impossible idea that Harry and Severus could work together in some manner, if they could but put aside their mutual animosity--a tall order indeed, I'll admit. However, I think that's precisely one of the many things that has to happen for Harry to be able to defeat Voldemort in book 7.
Harry is going to need help from someone, now that Albus is gone, that leaves Snape as the one in the best position to fill Harry in on the rest of Voldemort's backstory (if we need more of that). Snape is also well-connected in the Death Eaters and can give Harry all sorts of useful inside information on what they are doing, where they are, what their vulnerabilities are. He can help set a trap for Voldemort. There are so many possibilites, but the two of them have to quit being so stupid as to carry on an old feud that goes back to Snape's childhood, especially one that didn't involve Harry.
And on another level, as much of a prat as Harry was in HBP, his behaviour was a reminder that he is not an adult. He has moved closer to adulthood, but he is still a teen, and teens don't always make good choices. If Harry had suddenly started being perfect and responsible throughout most of the book, we would be accusing Rowling of not being true to the character--Harry would suddenly be Hermione, instead of Harry. Instead, he was a typical 16 year old, sometimes showing the glimmer of the adult he will someday become. One day a sixteen year old will make seemingly wise, very grown-up choices, and the next, they are back to being irresponsible, acting like spoiled selfish four year olds. To expect something different from Harry is to ask that he becomes a super-hero sort of character, and that's not at all what Rowling is writing. She has created Harry as a real person, with a good heart, but one who is not perfect and who can let his new image of himself turn to arrogance.
It was very hard to watch Harry doing some of the same thoughtless things that his father and Sirius had done when they were fifteen--they were bullying prats and not admirable at all. But I don't think we should be that surprised by it--Harry will go back to being himself. It works that way with some people; it's as though they have to get all the nastiness out of their system and they do it all in one year. Harry seems to have done that in HBP.
By the end of HBP (which I really see as the middle of the last part of the story), Harry is strong enough to stand up to Scrimgeour, and even to Professor McGonagall. He has a clear purpose ahead.
I think in book 7, something will happen to make Harry realize that he doesn't (and didn't) have all the answers about Draco or about Severus. And through that realization, Harry will gain the wisdom that he was lacking in Half-Blood Prince. Just what that will be, I've no idea. But Jo Rowling has led us this far along Harry's path, and I trust that she will get us to the end in a way that will show Harry as the true, pure-of-heart hero that we met in Philosopher's Stone nearly ten years ago.