What's up with Order of the Phoenix in the highest spot, though? I thought it was easily one of the worst of the series, and Goodreads ratings more or less agree with me, ranking only Chamber of Secrets lower.
For example: https://www.goodreads.com/list/show/1.Best_Books_Ever
#2 on that list. I always wondered the same, but could never reach a conclusion why it seemed like it was always rated above the rest of the series.
It is definitely the one that turned the series from "saving the school" to "saving the world" and the series made a sharp turn after that one. That's the best reason I could come up with.
From personal experience, it seems that more people find it to be the best than the worst, but there's a lot of disagreement.