Gasp! Spoilers!
I've been having an ongoing
argumentdiscussion with warpus about it being okay for adults to read books marketed for children, specifically the HP books.
My take on it is that people should read whatever they want to read, and to hell with what the marketing division or booksellers or reviewers say.
I still re-read my Archie comics and Alfred Hitchcock and The Three Investigators novels (the latter were marketed to teenage boys; I got hooked on them around age 10 or so, and I've belonged to a Yahoo! group for this particular mystery series for many years - most of the members of said group are easily at least 40-50 years old). The Fighting Fantasy gamebook series was likewise marketed to male teenage gamers, yet I daresay that it's likely that the majority of the members of the FF forum I belong to are well out of our teens.
In school, I always read several grades above where I was, and it was maddening to have to wait until I was 13 and could take books out of the adult section of the library (bigger selection of science fiction books than the kids' section).
About spoilers: I stopped giving a damn about spoiling stuff for other people when "they" stopped giving a damn that I didn't run out and watch the latest Star Wars movie within the first 3 days after its release, and so blabbed about Han Solo's death. When I read that, I figured, what's the point of watching the movie? And is it really a spoiler if the book came out 17 years ago and the characters are (some, anyway) basically mainstream knowledge?
First time, or are you re-reading? OOTP is probably my least favorite, though it has its moments -- mostly involving Gred and Forge. I so hate hate hate Umbridge.
Scary true story: The current Minister of Education in my province, Adriana LaGrange, has the attitude of Betsy DeVos and the personality of Umbridge. She even physically resembles Umbridge to the extent that there are memes posted on her FB page of her face 'shopped onto Umbridge's body... and if you didn't know the body belonged to a movie character, you'd almost think it was a real picture.