This is the third in the Harry Potter books and is about as good as the first two. It sticks too close to the formula of the first two books, although it manages to have an ending with at least some ambiguity in it. I still find it strange that the books start in a very Roald Dahl kind of style and become almost pure fantasy adventure by the end, so you have to slightly shift your suspension of disbelief as it goes along.
Rowling is a competent children's author. The book are reliable. They are good but not great. For instance, I think that they are inferior to both the Hunger Games trilogy and His Dark Materials. They could use more description and more complex character development. But they are definitely not trash.
I continue to not entirely understand why they became such a huge sensation. They are very, very readable, though.