There is little substance and character development. We are introduced to Harry by seeing him neglected in a closet, and with a persistent person sending him a letter. We then find out he's a very important person/hero for his talents and blood, and yet they could not be bothered to send more than a letter. Harry never acts on anything-- he merely reacts to what happens around him. None of his actions was made by him, he only acts in response to things that happen-- once, there was a conversation where it was only his friends talking and he was.. doing nothing, simply observing the conversation and staring at the wall until his friend addressed him.
Harry Potter and the big villain has literally NO character development. The evil guy is evil just to make evil turmoil and stuff in the series. Harry is just a shell-- he has no character and can't even morally react to anything. His owl has more personality.
Along with the terrible character development, there is a terrible plot. What do you expect when all the main characters are just a chess piece to make a "plot"?
The writing is also horrible too. Why do I want to observe Harry staring at his textbook and being unable to study for a whole two and a half pages when this could have been summarized in "Harry tried to study, spending time hunched over at his desk, staring at the pages that his mind refused to register. He closed his textbook, turned out the lights, and sat on his bed." It took two and a half pages to convey literally the same thing that does not further the plot or promote character development. It does set a mood, but the above sentences do the exact same thing.
td;lr This series has hollow main characters, and half-baked plots due to this. The writing is bland and full of fluff that could be condensed ten times. There is no speed in this book, the popularity is just exposure. 100% do not recommend.