Why people are so readily disappointed in J.K. Rowling

I've followed fandom through three Harry Potter releases, and every time people have been vastly disappointed in some aspect or another of the book, even if they enjoyed it as a whole.

I think this is because of Prisoner of Azkaban.

"But that one's my favourite!" you're protesting. Exactly.

Prisoner of Azkaban kicks ass. Characters who were mentioned in passing in previous books suddenly become key. There's a plot twist we never could have guessed with all kinds of clues laid out in front of us. The darkness hasn't fallen yet (in fact, there's no Voldy whatsoever in this book) so despite the lurking Dementors we get to enjoy the full whimsy of the wizarding world; adding to this whimsy is the time Harry gets to spend independently in Diagon Alley and the visits to Hogsmeade. There are multiple kick-ass Quidditch games. There's more cool and advanced magic, from the Patronus to the Marauder's Map. And then, in a thrilling, action-packed final sequence, everything from the Sirius Black plot to Hermione's odd behaviour to Prof. Lupin's illness several months ago to Ron's pet rat wraps up in a tight yet expositionary plot resolution that also provides us with extensive background on Harry's parents.

The problem is that this has raised our expectations to impossibly high levels. We now want every character mentioned in passing, from Mark Evans to the Giant Squid, to play some crucial role. We now want to know about the full history of everyone we meet, and expect equal amounts of insight on Harry's history. We now want every quirk of odd behaviour to have some key role in the ultimate plot. And we want it to all be fun and whimisical and kick-ass at the same time.

But this is impossible. The plot requires darkness, over 200 characters have had speaking roles (according to the guy who does the audiobooks), and we do need to resolve the plot rather than give the complete history of everything. There simply isn't room to give a full role to every single name and fully explain every odd twitch.

But we've had 10 years with these books, rereading, analyzing, theorizing, ficcing. We've had plenty of time to grow attached to Florean Fortescue or become deeply invested in identifying the Heir of Hufflepuff or created an entire universe around what Dudley saw when attacked by Dementors. Everyone has their own little corner of the Potterverse to which they are attached, about which they wanted full background, which they wanted to play a key role in the resolution of the overall plot arc. We've been developing our little hopes and dreams for the series for 10 years, and JKR cannot possibly meet them all.