system
Given the following post, respond as if you're commenting on Reddit:
human
[Opinion] The fifth Harry Potter book is the best in the series. CMV

Up until recently, I hold the view that I'm pretty sure most Potter fans have; that The Order of the Phoenix is the worst book because it is so long and Harry is so angsty and unlikeable.

However, my friends presents a good argument of why OotP is the *best* book out of the seven. Here are his arguments:

1. The truth about the marauders. In the third book, we are presented with an idealized view of what James Potter and his friends were like, but now, with the Snape's Worst Memory chapter, we find out that Snape is *right* about Harry's father being arrogant. The implications of the whole "You're so much like your father" idea are completely flipped from positive to negative.

2. OotP also introduces the idea that not all characters are black/white, good/bad. Harry, with his childlike inexperience, theorizes to Sirius that Umbridge is a Death Eater, but Sirius explains to him that not all bad people are death eaters. Similarly, just because James Potter is a bully to Snape, it doesn't mean he's necessarily a bad person.

3. Harry is the villain, and this is really cool. This is the first time Harry is lashing out at Ron and Hermione, instead of Ron and Hermione bickering with each other, like in the third book. He foolishly and childishly leads Dumbledore's Army into the Department of Mysteries, forcing the Order to intervene and save them. When Sirius dies, it's *Harry's fault*. Harry is broken down as a character in OotP so that he can be rebuilt in HBP, with the tests Dumbledore gives him.

Overall, OotP is the book where previous conceptions are broken down, the kids' childlike wonder ends up biting them in the ass for the first time (in the Department of Mysteries), and the whole trope of Harry going on adventures and succeeding in the end in a climactic battle is over. OotP is the book where we find out Harry is not a kid anymore, so that HBP can turn them into adults which they need for DH.
gpt
I personally think the Order of the Phoenix sets up the course of the events for the best book in the series, the Empire Strikes Back of the series, The Half Blood Prince. 

Using your points (which are very good and poignant mind you) let's see how we are set up for this work. 

> The truth about the marauders. In the third book, we are presented with an idealized view of what James Potter and his friends were like, but now, with the Snape's Worst Memory chapter, we find out that Snape is right about Harry's father being arrogant. The implications of the whole "You're so much like your father" idea are completely flipped from positive to negative.

Harry receives more truth in the sixth book about his life, the fact that the prophecy may not actually be about him. It might be in reference to Neville. We learn throughout the course of the books that Harry is the chosen one by chance. But, we start to question if he really is the chosen one. There are two individuals who have the same exact qualifications to be the one to defeat He Who Must Not Be Named. This is a huge deal, because if he's not the chosen one all of his sacrifices and all of what others sacrificed for him would have meant squat. 

> OotP also introduces the idea that not all characters are black/white, good/bad. Harry, with his childlike inexperience, theorizes to Sirius that Umbridge is a Death Eater, but Sirius explains to him that not all bad people are death eaters. Similarly, just because James Potter is a bully to Snape, it doesn't mean he's necessarily a bad person.

It is in this book we truly get the depth of Snape's character, and close to the end of the book we're convinced, utterly convinced, that's he's a good guy. He had saved Harry time and again, he was in love with Harry's mother, the works. But, everything is turned on its head when the man we started to root for killed the person that Harry counted on the most, Dumbledore. 

> Harry is the villain, and this is really cool. This is the first time Harry is lashing out at Ron and Hermione, instead of Ron and Hermione bickering with each other, like in the third book. He foolishly and childishly leads Dumbledore's Army into the Department of Mysteries, forcing the Order to intervene and save them. When Sirius dies, it's Harry's fault. Harry is broken down as a character in OotP so that he can be rebuilt in HBP, with the tests Dumbledore gives him.

Harry continues to act in a more villanous way in this book. He uses a spell that he doesn't know what it could do on another student, Draco. He nearly kills him as a result. It is here where we can see what Harry is willing to do to succeed, and that's an incredibly scary proposition. 

But, there is a more important facet to book six which matters so much moreso. 

- The bad guys win.