I just read "The Great Gatsby" for the first time (somehow never read it in school, don't know why...) and though it was a great story, I couldn't figure out what was so 'classic' about it.
I never liked "Emma" by Jane Austen, though I liked her other stuff. I found it tiresome and boring in parts, and it distracted from the story.
Now, "Jonathan Strange and Mr. Norrell" was a great book, written by Susanna Clarke in 2005, and it read very much like an Austen novel, and just as wordy, but I was sucked in for all 800+ pages. Go figure.