Are you eager to explore the role of government in the Harry Potter universe and its conflicts with other aspects of the universe?
Perhaps isolation, as multiple characters are isolated for major periods of time in various ways?
The internal conflicts between the Golden Trio, as Ron and Hermione really begin to show the burden of being tied to Harry?
Perhaps the theme of adolescent romance, focusing on its tendency to be messy?
Or perhaps power, as we are introduced to new ways in-universe that it can be attained and abused?
Maybe you have your own theme you'd love us to keep any eye on...