We invert the last question--so instead of a book you've really hated that friends recommended highly to you, now we have a book you ended up liking a great deal, that friends and such panned.
I'd have to go with the fourth part (book) of Gulliver's Travels. Back in junior high (which for those of you who aren't USian, means about twelve to fourteen years of age) I read the version in my school library. It consisted of the first three parts of GT, but not the controversial fourth part in which Swift portrayed a land where horses were noble, sensible, wise creatures, and humans were despicable brutes filled with low cunning. And nothing identifying what was missing got mentioned anywhere on the school copy.
Of course, I had to mention what a fascinating fourth section it had in a book review, which led to a furious teacher who acted as though I'd stolen her virginity (which I suspect was still intact in her sixties), and an administration that threatened me with suspension. Nothing came of it, but it certainly demonstrated several curious reasons people have for bowdlerizing the writings of others, and passing it off as accurate.
Over to you.