Sword in the Stone. I watched it last week, and I was so bored. I couldn't get into the story at all, and I didn't watch the end (mainly because Megavideo ran out, and I couldn't find the ending on YouTube, but that's beside the point!). It felt too inconsistent of a plot.
I would also say Black Cauldron, which I just finished. Gurgi was annoying. Very annoying. Despite it being the most expensive animated film at the time, the animation wasn't really all that good (compared to a few previous films. The animation for the past few films haven't been very amazing, but they weren't the most expensive animated films for their time as well). I couldn't really feel for any of the characters either.
Dinosaur, I won't even watch, because I don't like dinosaurs. So that's a given for me!