Biggest negative surprise was Country Bear Jamboree-I'd heard that was a Disney classic and might have long lines, so I considered myself fortunate to get in with little wait. Boy, was I disappointed-"I wanted to see this?" Another one was Astro-Orbiter. After 9 trips to WDW, I'd never ridden this and was so excited that I was finally going to do it! Scared me so much-afterwards I was laughing/crying so hard! To this day, DH won't let me live down the "great idea" I had to ride Astro Orbiter.
I think my biggest positive surprise has been Animal Kingdom in general. I know it's not everyone's favorite-matter of fact, there had been plenty of negative posts (boring, half-day park, etc.). I only went the first time to say I'd been and to weigh in with an opinion. Well, I love it! DH and I could spend hours just on Gorilla Falls Trail and Maharaja Jungle Trek. And we swear we're going to run into the Griswolds on vacation in C&H Dinorama sometime.